/// <summary>
/// This function is used to find the evaluation plan for the Query
/// - It avoids multiple recalculations
/// - It provides a step by step method for evaluating the Query
/// - It is a modified form of the original text-book evaluator
/// - My algorithm gets the plan without completely converting the expression to postfix
/// </summary>
/// <returns>A dictionary with the evaluation plan</returns>
public Dictionary<string, Field> FindEvalPlan()
{
//Required for getting the plan without having to convert to postfix
Stack<char> boolOpr = new Stack<char>();
Stack<string> boolOpd = new Stack<string>();
//Stores the evaluation plan as a <key, value> pair for easy access
EvalPlan = new Dictionary<string, Field>();
//Check every element in the Query
foreach (var i in Query)
{
if (i != ' ')
{
//Checking between operator and operand
if (prec.Contains<char>(i) == false)
{
//Operands are pushed into the operand queue
boolOpd.Push(i.ToString());
//The first occurances are used for generating test-cases
//So, they form a part of the evaluation plan
Field columnField = new Field();
if (boolOpd.Count != 0 && EvalPlan.Keys.Contains(boolOpd.Peek()) == false) { EvalPlan.Add(boolOpd.Peek(), columnField); }
}
else
{
//If the character is a valid symbol at a valid position
if (i != '(' && (boolOpr.Peek() != '(' || FindPrec(boolOpr.Peek()) <= FindPrec(i)))
{
//when the precedance becomes less then do evaluation plan generation
while (boolOpr.Peek() != '(' && FindPrec(boolOpr.Peek()) <= FindPrec(i))
{
//Get the plan according to the operator
Field columnField = new Field();
if (boolOpr.Peek() == '¬')
{
columnField.rightOpd = boolOpd.Pop();
columnField.fieldOpr = boolOpr.Pop();
boolOpd.Push("(" + " " + columnField.fieldOpr + " " + columnField.rightOpd + " " + ")");
}
else
{
columnField.rightOpd = boolOpd.Pop();
columnField.fieldOpr = boolOpr.Pop();
columnField.leftOpd = boolOpd.Pop();
boolOpd.Push("(" + " " + columnField.leftOpd + " " + columnField.fieldOpr + " " + columnField.rightOpd + " " + ")");
}
//If the plan was not already generated then add it
//Otherwise, discard to avoid redundancy
if (boolOpd.Count != 0 && EvalPlan.Keys.Contains(boolOpd.Peek()) == false) { EvalPlan.Add(boolOpd.Peek(), columnField); }
}
//If the character is ')' remove its corresponding '(' to balance the equation
if (i == ')') { boolOpr.Pop(); } else { boolOpr.Push(i); }
}
else { boolOpr.Push(i); } //Operators with higher precedance are simpley pushed into the operator stack
}
}
}
return EvalPlan;
}
/// <summary>
/// This constructor initializes the class
/// </summary>
/// <param name="data">The data for the nodes from the evalPlan</param>
/// <param name="result">This is a string that represents the result of the nodes operation</param>
/// <param name="yOffset">The yOffset from the top that indicates the depth of the node</param>
/// <param name="xOffset">The position of the node along the x - axis</param>
public TreeNode(Field data, string result, int yOffset, int xOffset)
{
this.data = data;
this.result = result;
this.yOffset = yOffset;
this.xOffset = xOffset;
InitializeGraphics();
}
