public static Stack <Token> GetPostfixExpression(List <Token> tokens)
{
Stack <Token> postfixExpression = new Stack <Token>();
Stack <Token> operationsStack = new Stack <Token>();
for (int i = 0; i < tokens.Count; i++)
{
Token currentToken = tokens[i];
switch (currentToken.Type)
{
case TOKEN_TYPE.VARIABLE:
case TOKEN_TYPE.CONST:
{
postfixExpression.Push(currentToken);
break;
}
case TOKEN_TYPE.BINARY_OPERATION:
{
if (operationsStack.Count == 0)
{
operationsStack.Push(currentToken);
}
else if (operationsStack.Peek().Type == TOKEN_TYPE.OPENING_BRACKET)
{
operationsStack.Push(currentToken);
}
else
{
Operation peekOp = OperationsManager.GetOperationByToken(operationsStack.Peek());
Operation currentOp = OperationsManager.GetOperationByToken(currentToken);
if (currentOp.Priority > peekOp.Priority)
{
operationsStack.Push(currentToken);
}
else
{
while (operationsStack.Peek().Type != TOKEN_TYPE.OPENING_BRACKET &&
currentOp.Priority <= peekOp.Priority)
{
postfixExpression.Push(operationsStack.Pop());
if (operationsStack.Count == 0 || operationsStack.Peek().Type == TOKEN_TYPE.OPENING_BRACKET)
{
break;
}
peekOp = OperationsManager.GetOperationByToken(operationsStack.Peek());
}
operationsStack.Push(currentToken);
}
}
break;
}
case TOKEN_TYPE.UNARY_OPERATION:
{
operationsStack.Push(currentToken);
break;
}
case TOKEN_TYPE.OPENING_BRACKET:
{
operationsStack.Push(currentToken);
break;
}
case TOKEN_TYPE.CLOSING_BRACKET:
{
while (operationsStack.Peek().Type != TOKEN_TYPE.OPENING_BRACKET)
{
postfixExpression.Push(operationsStack.Pop());
}
operationsStack.Pop(); // remove opening bracket from operations stack
break;
}
default:
{
break;
}
}
}
while (operationsStack.Count > 0)
{
postfixExpression.Push(operationsStack.Pop());
}
postfixExpression = new Stack <Token>(postfixExpression); // reverse stack
return(postfixExpression);
}