/// <summary>
/// Builds the tree also has a stack that we'll use to
/// keep track of the list's items. Shunting algorithm and precedence
/// will now be applied right away before items are read/to tree.
/// Observe the following algorithm. We use a regular expression to store the possible combinations (-,/,+,*,(,))
/// Symbols are partitoned out using the regular expression. Then we throw the entire list through shunting algorithm
/// We then iterate through the list returned and use the stack to push,pop out items accordingly.
/// </summary>
/// <param name="expression"></param>
/// <returns></returns>
private Node BuildTree(string expression)
{
var nodeStack = new Stack <Node>();
string pattern = @"([-/\+\*\(\)])";
var tokens = Regex.Split(expression, pattern).Where(s => s != String.Empty).ToList <string>();
foreach (var tok in ShuntingAlgo(tokens))
{
if (Char.IsLetter(tok[0]))
{
nodeStack.Push(new VariableNode(tok));
}
else if (Char.IsDigit(tok[0]))
{
nodeStack.Push(new ValueNode(Double.Parse(tok)));
}
else
{
var on = new OperatorNode(tok[0]);
on.right = nodeStack.Pop();
on.left = nodeStack.Pop();
nodeStack.Push(on);
}
}
root = nodeStack.Pop();
return(root);
}
// recursively evaluates tree
private double RecursiveEvaluate(Node root)
{
OperatorNode operatorHolder = new OperatorNode(' ');
ConstantNode constantHolder = new ConstantNode(0);
VariableNode variableHolder = new VariableNode(string.Empty);
double num = 0;
if (root is OperatorNode)
{
// if node is operator, evaluate left and right subtrees
operatorHolder = (OperatorNode)root;
return(Operation(RecursiveEvaluate(root.Left), RecursiveEvaluate(root.Right), operatorHolder.Op));
}
else if (root is VariableNode)
{
// if node is variable, return value stored in variable
variableHolder = (VariableNode)root;
num = Variables[variableHolder.Name];
return(num);
}
else
{
// if node is constant, return value of constant
constantHolder = (ConstantNode)root;
num = constantHolder.Value;
return(num);
}
}
/// <summary>
/// Builds the tree and has cases that it'll watch out for
/// </summary>
/// <param name="expression"></param>
/// <returns></returns>
Node BuildTree(string expression)
{
double val;
for (int i = expression.Length - 1; i >= 0; i--)
{
switch (expression[i])
{
case '+':
case '-':
case '*':
case '/':
OperatorNode newbie = new OperatorNode(expression[i]);
if (root == null)
{
root = newbie;
}
newbie.left = BuildTree(expression.Substring(0, i));
newbie.right = BuildTree(expression.Substring(i + 1));
return(newbie);
}
}
if (Double.TryParse(expression, out val))
{
return(new ValueNode(val));
}
else
{
return(new VariableNode(expression));
}
}
private double Evaluate(Node node)
{
if (node != null)
{
if (node is OperatorNode)
{
OperatorNode opNode = node as OperatorNode;
double evaluation = opNode.Evaluate();
return(evaluation);
}
if (node is ConstantNode)
{
ConstantNode constNode = node as ConstantNode;
return(constNode.Value);
}
if (node is VariableNode)
{
VariableNode varNode = node as VariableNode;
return(this.Variables[varNode.Name]);
}
}
return(0);
}
/// <summary>
/// Places a new node into the expression tree from the currentNode in either the left or right branches.
/// </summary>
/// <param name="newNode"> The node being inserted. </param>
/// <param name="currentNode"> The current position in the expression tree. </param>
/// <returns> True of false depending on if the node could be inserted. Helps TraverseTree() with recursion. </returns>
private bool InsertNode(Node newNode, Node currentNode)
{
OperatorNode positionNode = currentNode as OperatorNode;
ConstantNode constNode = newNode as ConstantNode;
OperatorNode opNode = newNode as OperatorNode;
VariableNode varNode = newNode as VariableNode;
// Right first to match the order of the expression stack.
if (positionNode.Right == null)
{
if (opNode != null)
{
// Making sure nothing is in the new branches as the tree is being made.
opNode.Left = null;
opNode.Right = null;
positionNode.Right = opNode;
}
else
{
if (varNode != null)
{
constNode = new ConstantNode()
{
Value = this.Variables[varNode.Name]
};
}
positionNode.Right = constNode;
}
return(true);
}
else if (positionNode.Left == null)
{
if (opNode != null)
{
// Making sure nothing is in the new branches as the tree is being made.
opNode.Left = null;
opNode.Right = null;
positionNode.Left = opNode;
}
else
{
if (varNode != null)
{
constNode = new ConstantNode()
{
Value = this.Variables[varNode.Name]
};
}
positionNode.Left = constNode;
}
return(true);
}
return(false);
}
/// <summary>
/// Evaluate:
/// This function is used to evaluate the expression tree. This logic is given to
/// us in our Etree.c lecture notes. It takes in an ExpressionTreeBaseNode param.
/// then tries to cast it as a ConstantNode, VariableNode, or OperatorNode. Based
/// on what the node type is (see ExpressionTreeNodeFactory) it will return a value
/// to be evaluated. (all root nodes should be operators)
/// </summary>
/// <param name="node"></param>
/// <returns></returns>
private double Evaluate(ExpressionTreeBaseNode node)
{
ConstantNode constantNode = node as ConstantNode;
if (constantNode != null)
{
return(constantNode.Value);
}
// as a variable
VariableNode variableNode = node as VariableNode;
if (variableNode != null)
{
return(variableDictionary[variableNode.Name]);
}
// it is an operator node if we came here
OperatorNode operatorNode = node as OperatorNode;
if (operatorNode != null)
{
// but which one?
switch (operatorNode.Operator)
{
case '+':
return(Evaluate(operatorNode.Left) + Evaluate(operatorNode.Right));
case '-':
return(Evaluate(operatorNode.Left) - Evaluate(operatorNode.Right));
case '*':
return(Evaluate(operatorNode.Left) * Evaluate(operatorNode.Right));
case '/':
try
{
return(Evaluate(operatorNode.Left) / Evaluate(operatorNode.Right));
}
catch (DivideByZeroException e)
{
Console.Write(e.Message);
Console.ReadLine();
}
break;
case '^':
return(Math.Pow(Evaluate(operatorNode.Left), Evaluate(operatorNode.Right)));
default: // if it is not any of the operators that we support, throw an exception:
throw new NotSupportedException(
"Operator " + operatorNode.Operator.ToString() + " not supported.");
}
}
throw new NotSupportedException();
}
/// <summary>
/// Finds where to insert a new node into the expression tree and calls InsertNode().
/// </summary>
/// <param name="newNode"> The node being inserted. </param>
/// <param name="currentNode"> The current position in the expression tree. </param>
/// <returns> True or false depending on if the node could be inserted. Helps with recursion of the tree. </returns>
private bool TraverseTree(Node newNode, Node currentNode)
{
OperatorNode positionNode = currentNode as OperatorNode;
OperatorNode rightNode = positionNode.Right as OperatorNode;
// Right first to match the order of the expression stack.
if (positionNode.Right != null && rightNode != null)
{
if (!this.TraverseTree(newNode, rightNode))
{
if (positionNode.Left is OperatorNode leftNode)
{
if (this.TraverseTree(newNode, leftNode))
{
return(true);
}
else
{
return(false);
}
}
else
{
return(this.InsertNode(newNode, currentNode));
}
}
}
else if (positionNode.Left != null)
{
if (positionNode.Left is OperatorNode leftNode)
{
if (this.TraverseTree(newNode, leftNode))
{
return(true);
}
else
{
return(false);
}
}
else
{
return(this.InsertNode(newNode, currentNode));
}
}
return(this.InsertNode(newNode, currentNode));
}
/// <summary>
/// Evaluates the expression tree's arithmetic.
/// </summary>
/// <returns>Returns the arithmetic calculation of the expression tree.</returns>
public double Evaluate()
{
if (this.head == null)
{
if (this.singleNodeString != null)
{
return(this.variables[this.singleNodeString]);
}
else
{
return(this.singleNodeDouble);
}
}
OperatorNode current = this.head; // A reference to the head of this expression tree.
return(this.EvaluateHelper(current)); // Return the result of the helper method.
}
private double Eval(BaseNode node)
{
//Evaluate based on the kind of node
ConstantNode constnode = node as ConstantNode;
if (constnode != null)
{
return(constnode.OpValue);
}
VariableNode varnode = node as VariableNode;
if (varnode != null)
{
// used to be a try/catch, but now we set every new variable to 0 when the tree is made, so there will always be a value to obtain.
return(variableDict[varnode.Name]);
}
OperatorNode opnode = node as OperatorNode;
if (opnode != null)
{
switch (opnode.Op)
{
case '+':
return(Eval(opnode.Left) + Eval(opnode.Right));
case '-':
return(Eval(opnode.Left) - Eval(opnode.Right));
case '*':
return(Eval(opnode.Left) * Eval(opnode.Right));
case '/':
return(Eval(opnode.Left) / Eval(opnode.Right));
}
}
return(0);
}
/// <summary>
/// Builds an expression tree from expression string.
/// Returns the root node of the expression tree.
/// </summary>
/// <param name="expression">Expression string.</param>
/// <returns>Root of built expression tree.</returns>
private ExpressionTreeNode BuildExpressionTree(string expression)
{
List <ExpressionTreeNode> postfixList = this.GetPostfixList(expression);
Stack <ExpressionTreeNode> stack = new Stack <ExpressionTreeNode>();
foreach (ExpressionTreeNode currNode in postfixList)
{
if (this.IsConstantNode(currNode) || this.IsVariableNode(currNode))
{
stack.Push(currNode);
}
else
{
OperatorNode currOpNode = currNode as OperatorNode;
currOpNode.Right = stack.Pop();
currOpNode.Left = stack.Pop();
stack.Push(currOpNode);
}
}
return(stack.Pop());
}
public override TreeNode FactoryMethod(string expression)
{
OpNodeFactory opNodeFactory = new ConcreteOpNodeFactory();
OperatorNode @operator = opNodeFactory.FactoryMethod(expression);
if (@operator != null)
{
return(@operator);
}
else
{
bool int_success = Int32.TryParse(expression, out int int_result),
double_success = Double.TryParse(expression, out double double_result);
if (int_success)
{
return(new ValueNode(int_result));
}
else
{
return(new ValueNode(double_result));
}
}
}
/// <summary>
/// Prints the content of the expression tree to the console.
/// </summary>
/// <param name="node">The head of the expression tree.</param>
/// <param name="result">The resultant string.</param>
private void PrintTreeHelper(OperatorNode node, string result)
{
// In-order traversal algorithm.
if (node.Left != null && node.Right != null)
{
// Check for OperatorNode or other node on left.
if (!this.IsOperatorNode(node.Left))
{
Console.Write(node.Left.Value);
result += node.Left.Value;
}
else
{
this.PrintTreeHelper((OperatorNode)node.Left, result);
}
// Print current node value.
Console.Write(node.Value);
result += node.Value;
// Check for OperatorNode or other node on right.
if (!this.IsOperatorNode(node.Right))
{
Console.Write(node.Right.Value);
}
else
{
this.PrintTreeHelper((OperatorNode)node.Right, result);
}
}
else
{
// Print the leaf's value.
Console.WriteLine(node.Value);
}
}
/// <summary>
/// GetNode:
/// returns a ExpressionTreeNode such based off of client specified parameters. Only supports
/// Constant, Variable, and Operator Nodes. All of which inherit from ExpressionTreeBaseNode.
/// </summary>
/// <param name="nodeType">
/// nodeType string will specify which kind of ExpressionTree Node the client wishes to instantiate
/// </param>
/// <param name="operation">
/// operation char specifies the operation the client wishes to pass into OperationNode constructor.
/// (Optional) If passed in with "C" or "V" it will not be used.
/// </param>
/// <returns> ExpressionTreeBaseNode </returns>
public ExpressionTreeBaseNode GetNode(string nodeType, string operation = "\0")
{
ExpressionTreeBaseNode node;
switch (nodeType)
{
case "C": /*constant*/
ConstantNode constantNode = new ConstantNode();
double result;
if (double.TryParse(operation, out result))
{
constantNode.Value = result;
}
node = constantNode;
return(node);
case "V": /*variable*/
VariableNode variableNode = new VariableNode();
variableNode.Name = operation;
node = variableNode;
return(node);
case "O": /*operator*/
char op = operation[0];
node = new OperatorNode(op);
return(node);
default: return(null);
}
}
/// <summary>
/// Better implementation that checks and evaluates off dict right away.
/// Evaluate is self explained that returns the value (new or assigned)
/// </summary>
/// <returns></returns>
private double Evaluate(Node node)
{
ValueNode constnode = node as ValueNode;
if (constnode != null)
{
return(constnode.OpValue);
}
VariableNode varnode = node as VariableNode;
if (varnode != null)
{
return(variableDict[varnode.Name]);
}
OperatorNode opnode = node as OperatorNode;
if (opnode != null)
{
switch (opnode.Op)
{
case '+':
return(Evaluate(opnode.Left) + Evaluate(opnode.Right));
case '-':
return(Evaluate(opnode.Left) - Evaluate(opnode.Right));
case '*':
return(Evaluate(opnode.Left) * Evaluate(opnode.Right));
case '/':
return(Evaluate(opnode.Left) / Evaluate(opnode.Right));
}
}
return(0);
}
/// <summary>
/// Takes a valid string expression and returns a postfix ordered list of expression tree nodes.
/// Uses Dijkstra's Shunting Yard algorithm.
/// </summary>
/// <param name="expression">Valid expression string.</param>
/// <returns>Postfix ordered expression tree node list.</returns>
private List <ExpressionTreeNode> GetPostfixList(string expression)
{
Stack <char> stack = new Stack <char>();
List <ExpressionTreeNode> postfixList = new List <ExpressionTreeNode>();
OperatorNodeFactory opFact = new OperatorNodeFactory();
char[] expressionArray = expression.ToArray <char>();
// loops over each char in expression string
for (int i = 0; i < expressionArray.Length; i++)
{
char currChar = expressionArray[i];
// if the current char is a left parenthesis, push to stack
if (currChar.Equals('('))
{
stack.Push(currChar);
}
// if the current char is a right parenthesis
else if (currChar.Equals(')'))
{
// while the top of the stack is not a left parenthesis, pop and add to list
while (!stack.Peek().Equals('('))
{
OperatorNode newOpNode = opFact.CreateOperatorNode(stack.Pop());
postfixList.Add(newOpNode);
}
stack.Pop(); // pop the left parenthesis from the top of the stack
}
// If the current char is a valid operator
else if (opFact.IsValidOperator(currChar))
{
// if the stack is empty or the next char is a left parenthesis
if (stack.Count <= 0 || stack.Peek().Equals('('))
{
stack.Push(currChar);
}
// otherwise the next char on the stack is an operator
else
{
OperatorNode currOpNode = opFact.CreateOperatorNode(currChar);
OperatorNode nextOpNode = opFact.CreateOperatorNode(stack.Peek());
// if curr operator has > precedence than the next operator, or equal precedence and right associativity
if (currOpNode.Precedence > nextOpNode.Precedence ||
(currOpNode.Precedence == nextOpNode.Precedence && currOpNode.Associativity == OperatorNode.Associative.Right))
{
stack.Push(currChar); // push the current operator on the stack
}
// if curr operator has < precedence than the next operator, or equal precedence and left associativity
else
{
// add the next operator to the list
stack.Pop();
postfixList.Add(nextOpNode);
i--;
}
}
}
// if the current char is a digit (0-9)
else if (char.IsDigit(currChar))
{
string constantString = currChar.ToString();
for (int j = i + 1; j < expressionArray.Length; j++)
{
currChar = expressionArray[j];
// if the next char is a digit, append to constant string
if (char.IsDigit(currChar))
{
constantString += currChar.ToString();
i++;
}
// otherwise the next char is not part of this number
else
{
break;
}
}
postfixList.Add(new ConstantNode(double.Parse(constantString))); // add the complete number to the list
}
// if the current char is a variable
else
{
string variable = currChar.ToString();
for (int j = i + 1; j < expressionArray.Length; j++)
{
currChar = expressionArray[j];
// if the next char is not an operator
if (!opFact.IsValidOperator(currChar))
{
variable += expressionArray[j].ToString();
i++;
}
// otherwise the next char is not part of this variable
else
{
break;
}
}
// add the complete variable to the list
postfixList.Add(new VariableNode(variable, ref this.variables));
// Add the name to variabelNames list if it is not already in it.
if (!this.variableNames.Contains(variable))
{
this.variableNames.Add(variable);
}
}
}
// pop and add the rest of the stack to the list
while (stack.Count > 0)
{
OperatorNode newOpNode = opFact.CreateOperatorNode(stack.Pop());
postfixList.Add(newOpNode);
}
return(postfixList);
}
/// <summary>
/// Initializes a new instance of the <see cref="ExpressionTree"/> class.
/// </summary>
/// <param name="expression">The arithmetic expression to be generated.</param>
public ExpressionTree(string expression)
{
bool isSingleNodeTree = true;
foreach (char op in this.Operators)
{
if (expression.Contains(op))
{
isSingleNodeTree = false;
break;
}
}
if (isSingleNodeTree)
{
try
{
this.singleNodeDouble = Convert.ToDouble(expression);
}
catch (Exception)
{
this.singleNodeString = expression;
}
return;
}
// Generate the postfix notation for the expression.
string[] postfixArray = this.ConvertToPostfix(expression);
// Declare local variables.
Node left, right;
OperatorNode center;
Stack <Node> nodeStack = new Stack <Node>();
ExpressionTreeFactory etf = new ExpressionTreeFactory();
// Iterate through each string in the postfix expression.
for (int i = 0; i < postfixArray.Length; i++)
{
string s = postfixArray[i];
// Check for an empty string.
if (s == string.Empty)
{
continue;
}
// Operator found!
if (s.Length == 1 && this.Operators.Contains(s[0]))
{
// Create a new node with the top two nodes of the stack
// as children and push it onto the top of the stack.
center = (OperatorNode)etf.CreateNode(s);
right = nodeStack.Pop();
left = nodeStack.Pop();
center.Left = left;
center.Right = right;
nodeStack.Push(center);
}
else
{
nodeStack.Push(etf.CreateNode(s)); // Push a non-operator node onto the stack.
}
}
// Set the new head of the expression tree.
this.head = (OperatorNode)nodeStack.Peek();
nodeStack.Pop();
}
/// <summary>
/// Evaluates the arithmetic logic of an expression tree.
/// </summary>
/// <param name="current">The head of the tree to be evaluated.</param>
/// <returns>Returns the evaluation of the expression tree.</returns>
private double EvaluateHelper(OperatorNode current)
{
// Both children are leaves.
if (!this.IsOperatorNode(current.Left) && !this.IsOperatorNode(current.Right))
{
double leftVal, rightVal;
if (this.IsVariableNode(current.Left))
{
leftVal = this.variables[current.Left.Value]; // Get left value from dictionary.
}
else
{
leftVal = Convert.ToDouble(current.Left.Value); // Get left value from left node.
}
if (this.IsVariableNode(current.Right))
{
rightVal = this.variables[current.Right.Value]; // Get right value from dictionary.
}
else
{
rightVal = Convert.ToDouble(current.Right.Value); // Get right value from right node.
}
return(current.Evaluate(leftVal, rightVal));
}
else if (!this.IsOperatorNode(current.Left))
{
// Only the right node is an operator node.
double leftVal;
if (this.IsVariableNode(current.Left))
{
leftVal = this.variables[current.Left.Value]; // Get left value from dictionary.
}
else
{
leftVal = Convert.ToDouble(current.Left.Value); // Get left value from left node.
}
return(current.Evaluate(leftVal, this.EvaluateHelper((OperatorNode)current.Right)));
}
else if (!this.IsOperatorNode(current.Right))
{
// Only the left node is an operator node.
double rightVal;
if (this.IsVariableNode(current.Right))
{
rightVal = this.variables[current.Right.Value]; // Get right value from dictionary.
}
else
{
rightVal = Convert.ToDouble(current.Right.Value); // Get right value from right node.
}
return(current.Evaluate(this.EvaluateHelper((OperatorNode)current.Left), rightVal));
}
else
{
// Both children are operator nodes.
OperatorNode leftNode = (OperatorNode)current.Left, rightNode = (OperatorNode)current.Right;
return(current.Evaluate(this.EvaluateHelper(leftNode), this.EvaluateHelper(rightNode)));
}
}
private ExpressionTreeBaseNode CreateExpressionTree(string expression)
{
Stack <ExpressionTreeBaseNode> operandStack = new Stack <ExpressionTreeBaseNode>();
int precidence = -1;
/**********************************************************************/
// we will parse the expression string into the expression tree here! //
/**********************************************************************/
int expressionIndex = 0;
for (; expressionIndex < expression.Length; expressionIndex++)
{
char currentChar = expression[expressionIndex];
//not an operator
if (!CheckOperatorPrecidence(currentChar, ref precidence))
{
switch (currentChar)
{
//Constant (double)
case ':':
string constantValue = "";
expressionIndex++;
//traverse expression to grab the entire constant (double), and store in constantValue
while (expressionIndex < expression.Length && expression[expressionIndex] != ':')
{
constantValue += expression[expressionIndex];
expressionIndex++;
}
//create new ConstantNode and pass in the corresponding Value prop.
ExpressionTreeBaseNode constantNode = nodeFactory.GetNode("C", constantValue);
//convert type to constant node to print the value
/*
* ConstantNode node = (ConstantNode)constantNode;
* Console.WriteLine("constantNode.Value = " + node.Value);
*/
operandStack.Push(constantNode); //push to operand stack
break;
//Variable (string)
case '{':
string variableName = "";
expressionIndex++;
//traverse expression to grab the entire constant (double), and store in constantValue
while (expressionIndex < expression.Length && expression[expressionIndex] != '}')
{
variableName += expression[expressionIndex];
expressionIndex++;
}
//create new VariableNode and pass in the corresponding Name prop.
ExpressionTreeBaseNode variableNode = nodeFactory.GetNode("V", variableName);
//convert type to constant node to set the default value
VariableNode tempNode = (VariableNode)variableNode;
SetVariable(tempNode.Name, 0.0);
operandStack.Push(variableNode); //push to operand stack
break;
}
}
//currentChar is an operator
else
{
//create new OperatorNode and pass in the corresponding operator prop.
ExpressionTreeBaseNode operatorNode = nodeFactory.GetNode("O", currentChar.ToString());
//convert type to constant node to print the value
OperatorNode tempNode = (OperatorNode)operatorNode;
//pop two operands off of the stack
ExpressionTreeBaseNode rightNode = operandStack.Pop();
ExpressionTreeBaseNode leftNode = operandStack.Pop();
//set operatornode left and right nodes.
tempNode.Left = leftNode;
tempNode.Right = rightNode;
operandStack.Push(tempNode); //push operator node onto stack
}
}
ExpressionTreeBaseNode expressionTreeRoot = operandStack.Peek(); //expression tree root is top of stack
operandStack.Pop(); //pop top of stack (root)
return(expressionTreeRoot);
}
/// <summary>
/// Edsger Dijkstra's Shunting Yard algorithm to convert an infix expression into postfix expression.
/// </summary>
/// <param name="infixExpression"> Infix expression. </param>
/// <returns> Postfix expression. </returns>
private Queue <Node> ShuntingYardAlgorithm(string infixExpression)
{
Queue <Node> postfixExpression = new Queue <Node>();
Stack <OperatorNode> operatorStack = new Stack <OperatorNode>();
for (int index = 0; index < infixExpression.Length;)
{
// Need to create substring until the first operator in the expression is reached.
string substring = string.Empty;
int substringIndex;
for (substringIndex = index; substringIndex < infixExpression.Length && !ExpressionTreeFactory.MatchesCharacter(infixExpression[substringIndex]); substringIndex++)
{
substring += infixExpression[substringIndex];
}
// If the substring is a number then turn that substring into one.
if (double.TryParse(substring, out double numSubstring))
{
postfixExpression.Enqueue(new ConstantNode()
{
Value = numSubstring
});
index = substringIndex;
}
else
{
if (ExpressionTreeFactory.MatchesOperator(infixExpression[index]))
{
OperatorNode op = ExpressionTreeFactory.CreateOperatorNode(infixExpression[index]);
try
{
// If there are operators on the operatorStack with higher precedence than op then they need to be removed from the stack and added to the postfixExpression first.
while (operatorStack.Peek().Precedence >= op.Precedence && operatorStack.Peek().Operator != '(')
{
postfixExpression.Enqueue(operatorStack.Pop());
}
}
catch
{
// Possible for there to be an empty operatorStack. In that case, nothing happens.
}
operatorStack.Push(op);
}
else if (infixExpression[index] == '(')
{
operatorStack.Push(new OperatorNode('(')
{
Precedence = 4
});
}
else if (infixExpression[index] == ')')
{
try
{
while (operatorStack.Peek().Operator != '(')
{
postfixExpression.Enqueue(operatorStack.Pop());
}
}
catch
{
throw new ArgumentException("Missing a left parenthesis");
}
operatorStack.Pop();
}
else
{
// If the substring cannot be parsed as a double (constant) or parentheses then it's a variable.
postfixExpression.Enqueue(new VariableNode()
{
Name = substring
});
if (!this.Variables.ContainsKey(substring))
{
this.SetVariable(substring, 0);
}
index = substringIndex - 1;
}
index++;
}
}
// End of the expression, popping all operators onto the queue
while (operatorStack.Count != 0)
{
if (operatorStack.Peek().Operator != '(')
{
postfixExpression.Enqueue(operatorStack.Pop());
}
else
{
throw new ArgumentException("Missing a right parenthesis");
}
}
return(postfixExpression);
}
public ExpressionTree(string expression)
{
this.expression = expression;
List <Node> postfixExpression = new List <Node>();
List <OperatorNode> operatorStack = new List <OperatorNode>();
string variable = string.Empty;
string integer = string.Empty;
string expressionString = string.Empty;
OperatorNode opNode;
// create postfix expression from given expression
// begin by building postfixExpression and operatorStack lists
for (int i = 0; i < expression.Length; i++)
{
if (variable != string.Empty && Char.IsLetterOrDigit(expression[i]))
{
variable += expression[i];
}
else if (Char.IsLetter(expression[i]))
{
variable += expression[i];
}
else if (variable == string.Empty && Char.IsDigit(expression[i]))
{
integer += expression[i];
}
else if (integer != string.Empty && Char.IsDigit(expression[i]))
{
integer += expression[i];
}
else if (!Char.IsLetterOrDigit(expression[i]) && (expression[i] != ')') && variable != string.Empty)
{
postfixExpression.Add(new VariableNode(variable)); // add variable to postfix expression
opNode = new OperatorNode(expression[i]);
// only do if operator stack is not empty
if (operatorStack.Count > 0)
{
bool overPrecedence = true;
// encountered operator or parenthesis, determine what happens next
while (overPrecedence == true && operatorStack.Count != 0)
{
// pop operators from operator stack and push onto list expression if precedence is greater than or equal to operator being pushed onto operator stack
if (operatorStack[operatorStack.Count - 1].Precedence <= opNode.Precedence)
{
postfixExpression.Add(operatorStack[operatorStack.Count - 1]);
operatorStack.RemoveAt(operatorStack.Count - 1);
}
else
{
overPrecedence = false;
}
}
}
operatorStack.Add(opNode); // push operator onto operator stack
variables.Add(variable, 0); // add variable to dictionary, initialize to 0
variable = string.Empty; // reset variable string to empty, prepare for new variable entry
}
else if (!Char.IsLetterOrDigit(expression[i]) && (expression[i] != ')') && integer != string.Empty)
{
postfixExpression.Add(new ConstantNode(double.Parse(integer))); // add integer to postfix expression
opNode = new OperatorNode(expression[i]);
if (operatorStack.Count > 0)
{
bool overPrecedence = true;
// encountered operator or parenthesis, determine what happens next
while (overPrecedence == true && operatorStack.Count != 0)
{
// pop operators from operator stack and push onto list expression if precedence is greater than or equal to operator being pushed onto operator stack
if (operatorStack[operatorStack.Count - 1].Precedence <= opNode.Precedence)
{
postfixExpression.Add(operatorStack[operatorStack.Count - 1]);
operatorStack.RemoveAt(operatorStack.Count - 1);
}
else
{
overPrecedence = false;
}
}
}
operatorStack.Add(opNode); // push operator onto operator stack
integer = string.Empty; // reset integer string to empty, prepare for new integer entry
}
else if (expression[i] == '(')
{
operatorStack.Add(new OperatorNode('('));
}
else if (expression[i] == ')' && variable != string.Empty)
{
postfixExpression.Add(new VariableNode(variable)); // add variable to postfix expression
if (!variables.ContainsKey(variable))
{
variables.Add(variable, 0); // add variable to dictionary, initialize to 0
}
variable = string.Empty; // reset variable string to empty, prepare for new variable entry
// while no left bracket found, pop operators from operator stack onto expression
while (operatorStack[operatorStack.Count - 1].Op != '(')
{
postfixExpression.Add(operatorStack[operatorStack.Count - 1]);
operatorStack.RemoveAt(operatorStack.Count - 1);
}
operatorStack.RemoveAt(operatorStack.Count - 1); // remove left bracket from operator stack
}
else if (expression[i] == ')' && integer != string.Empty)
{
postfixExpression.Add(new ConstantNode(double.Parse(integer))); // add integer to postfix expression
integer = string.Empty; // reset integer string to empty, prepare for new integer entry
// while no left bracket found, pop operators from operator stack onto expression
while (operatorStack[operatorStack.Count - 1].Op != '(')
{
postfixExpression.Add(operatorStack[operatorStack.Count - 1]);
operatorStack.RemoveAt(operatorStack.Count - 1);
}
operatorStack.RemoveAt(operatorStack.Count - 1); // remove left bracket from operator stack
}
else if (expression[i] == ')')
{
// while no left bracket found, pop operators from operator stack onto expression
while (operatorStack[operatorStack.Count - 1].Op != '(')
{
postfixExpression.Add(operatorStack[operatorStack.Count - 1]);
operatorStack.RemoveAt(operatorStack.Count - 1);
}
operatorStack.RemoveAt(operatorStack.Count - 1); // remove left bracket from operator stack
}
else if (expression[i] == '*' || expression[i] == '+' || expression[i] == '-' || expression[i] == '/')
{
operatorStack.Add(new OperatorNode(expression[i])); // adds operator to stack, only used when an operator appears after a ')'
}
// takes into account an expression of only one variable or one constant (ex. "x" or "12")
if ((i + 1) == expression.Length && variable != string.Empty)
{
variables.Add(variable, 0);
postfixExpression.Add(new VariableNode(variable));
}
else if ((i + 1) == expression.Length && integer != string.Empty)
{
postfixExpression.Add(new ConstantNode(double.Parse(integer)));
}
}
int operands = postfixExpression.Count; // keeps track of how many operands in expression
// pop the rest of the operators off of the operator stack
for (int j = 0; j < operatorStack.Count; j++)
{
int index = operatorStack.Count - 1;
postfixExpression.Add(operatorStack[index - j]);
}
Node curr = null; // used to keep track of what node we are on
int postIndex = postfixExpression.Count - 1;
List <Node> markers = new List <Node>();
// build tree based on postfixExpression
while (postIndex >= 0)
{
// setting first node
if (root == null)
{
root = postfixExpression[postIndex]; // set root to first node encountered in list
curr = root; // set tracker to root after it is created
postIndex -= 1;
}
else
{
if (postIndex >= 0)
{
// determine where next node needs to go based on positional criteria
if ((curr.Left != null) && (curr.Right != null) && markers.Count != 0 && postIndex == 0)
{
// Condition: if both left and right nodes are full, there are still markers in marker list, and we are now at the beginning of the postfixExpression
// Do: then work back through markers until we've reached needed position and place last node
while (curr.Left != null && curr.Right != null)
{
curr = markers[markers.Count - 1];
markers.RemoveAt(markers.Count - 1);
}
if (curr.Right == null)
{
curr.Right = postfixExpression[postIndex];
}
else if (curr.Left == null)
{
curr.Left = postfixExpression[postIndex];
}
postIndex -= 1;
}
else if (!(curr.Left is OperatorNode) && !(curr.Right is OperatorNode) && (curr.Left != null) && (curr.Right != null) && markers.Count != 0)
{
// Condition: if both left and right nodes are not operators, are not null, and there are markers still in marker list
// Do: then move back to the last node that has an open left or right and place next node in open position
while (curr.Left != null && curr.Right != null)
{
curr = markers[markers.Count - 1];
markers.RemoveAt(markers.Count - 1);
}
if (curr.Right == null)
{
curr.Right = postfixExpression[postIndex];
if (curr.Right is OperatorNode)
{
curr = curr.Right;
}
}
else if (curr.Left == null)
{
curr.Left = postfixExpression[postIndex];
if (curr.Left is OperatorNode)
{
curr = curr.Left;
}
}
postIndex -= 1;
}
else if (curr is OperatorNode && !(postfixExpression[postIndex] is OperatorNode) && !(postfixExpression[postIndex - 1] is OperatorNode))
{
// Condition: if we are currently on an operator node, and the next two nodes on postfixExpression are not operators
// Do: then add these two nodes to the right and left of our current node
curr.Right = postfixExpression[postIndex];
curr.Left = postfixExpression[postIndex - 1];
postIndex -= 2;
}
else if (curr is OperatorNode && postfixExpression[postIndex] is OperatorNode && curr.Right == null)
{
// Condition: if we are currently on an operator node, and the next node in the expression is an operator, and the current node's right is empty
// Do: then add a marker to marker list that tracks current node, add node from expression to right of current node, and move current to the node we just placed
markers.Add(curr); // drop marker to come back to
curr.Right = postfixExpression[postIndex];
curr = curr.Right;
postIndex -= 1;
}
else if ((curr is OperatorNode) && (postfixExpression[postIndex] is OperatorNode) && (curr.Left == null))
{
// Condition: if our current node is an operator, and the next node in expression is an operator, and the current node's left is empty
// Do: then add a marker to marker list that tracks current node, add node from expression to left of current node, and move current to the node we just placed
markers.Add(curr);
curr.Left = postfixExpression[postIndex];
curr = curr.Left;
postIndex -= 1;
}
else
{
// Condition: if none of the other conditional statements matched with conditions
// Do: then place the next node in expression to the right of our current node
curr.Right = postfixExpression[postIndex];
postIndex -= 1;
}
}
else
{
curr.Right = postfixExpression[postIndex]; // add node to right
postIndex -= 1;
}
}
}
}