/// <summary>
/// create a nod.
/// </summary>
/// <param name="name"> name.</param>
/// <returns> node .</returns>
private ExpressionTreeNode CreateNode(string name)
{
if ((name[0] >= 48 && name[0] <= 57) || (name.Length > 1 && name[0] == '-'))
{
/* First character is a number: Constant Node */
if (int.TryParse(name, out int value))
{
return(new ConstantNode(value));
}
else
{
return(null);
}
}
else if (name.Length == 1 && this.IsOperator(name[0]))
{
/* Operator Node */
return(OperatorNodeFactory.CreateNewNode(name[0]));
}
else
{
/* Variable Node */
return(new VariableNode(name));
}
}
// post: helps returns a node in the expression tree based on the given expression
// int index - the index of the lowest precedence operator in the expression
// string expression - the given english expression that may consist of letters, numbers, and operators
private static BaseNode GetNodeHelper(int index, string expression)
{
if (index != -1)
{
BinaryOperatorNode node = OperatorNodeFactory.CreateOperatorNode(expression[index]);
node.Right = GetNode(expression.Substring(index + 1));
node.Left = GetNode(expression.Substring(0, index));
return(node);
}
else if (index == -2)
{
throw new System.ArgumentException("Too many or too few parentheses", "Invalid expression");
}
return(BuildVariableNode(expression));
}
/// <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);
}
