protected string DoShuntingYardAlgorithm(TokenizerInterface tokenizer)
{
// I have referred shunting-yard algorithm https://en.wikipedia.org/wiki/Shunting-yard_algorithm
Token token = tokenizer.GetNextToken();
Token lastToken = null;
bool first = true;
bool afterOpenParenthesis = false;
while (token.Type != TokenType.None)
{
// Token is a number, add it to the output queue.
if (IsDigit(token))
{
AddToOutput(token.GetValueAsString());
}
else if (token.GetValueAsString() == ".")
{
AddToOutput(token.GetValueAsString());
}
// Token is a left parenthesis "(", push it onto the stack.
else if (token.GetValueAsString() == "(")
{
operatorStack.Push(token.GetValueAsString());
}
// Token is a right parenthesis ")"
else if (token.GetValueAsString() == ")")
{
string lastOperation = operatorStack.Peek();
while (lastOperation != "(")
{
AddToOutput(operatorStack.Pop());
lastOperation = operatorStack.Peek();
}
// Pop the left parenthesis from the stack
operatorStack.Pop();
// Mark parenthesis flag to avoid false unary operation detection
afterOpenParenthesis = true;
}
// Token is an operator, o1
else if (IsOperator(token))
{
string currentOperation = token.GetValueAsString();
// check for negation at the beginning of the input formal.
if (first && currentOperation == "-")
{
currentOperation = "m";
}
// check for plus sign at the beginning of the input formal.
else if (first && currentOperation == "+")
{
currentOperation = "p";
}
else if (operatorStack.Count > 0)
{
string lastOperation = operatorStack.Peek();
// If parenthesis flag is set avoid false unary operation detection
if (!afterOpenParenthesis)
{
// check for negation direct after a '(' or after another operator.
if ((IsOperator(lastOperation) || lastOperation == "(") && currentOperation == "-" && lastOperation != "p" && lastOperation != "m" && !IsDigit(lastToken))
{
currentOperation = "m";
}
// check for plus sign direct after a '(' or after another operator.
if ((IsOperator(lastOperation) || lastOperation == "(") && currentOperation == "+" && lastOperation != "p" && lastOperation != "m" && !IsDigit(lastToken))
{
currentOperation = "p";
}
}
//while there is an operator token, lastOperation
while (IsOperator(lastOperation))
{
// Check precedence of operators
if (IsLeftAssociative(currentOperation) && LessOrEqualPrecedence(currentOperation, lastOperation) ||
IsRightAssociative(currentOperation) && LessPrecedence(currentOperation, lastOperation))
{
AddToOutput(operatorStack.Pop());
if (operatorStack.Count == 0)
{
break;
}
else
{
lastOperation = operatorStack.Peek();
}
}
else
{
break;
}
}
}
operatorStack.Push(currentOperation);
// Reset parenthesis flag.
afterOpenParenthesis = false;
}
lastToken = token;
token = tokenizer.GetNextToken();
first = false;
}
// If there are still operator tokens in the stack:
while (operatorStack.Count > 0)
{
// Pop the operator onto the output queue.
AddToOutput(operatorStack.Pop());
}
return(CreateOutput(output));
}
public InfixToPostfixConverter(TokenizerInterface tokenizer)
{
myTokenizer = tokenizer;
}