/// <summary>
/// Check if the expression needs to be tokenised in multiple cases
/// e.g. Check if there is unary, check if parenthesis has multiply symbol
/// </summary>
private List <string> CheckIfTokenised(char[] tokenList)
{
List <string> newList = new List <string>();
for (int i = 0; i < tokenList.Length; i++)
{
char token = tokenList[i];
if (newList.Count != 0)
{
string topNewToken = newList[newList.Count - 1];
// If more than one digit, then combine with the previous digit
if (char.IsDigit(token) && tokenChecker.IsNumber(topNewToken))
{
newList[newList.Count - 1] += token;
}
// If there is an X after a number
else if (token.Equals('x') && tokenChecker.IsNumber(topNewToken))
{
newList.Add("*");
newList.Add(token.ToString());
}
// Add multiply symbol if the token meets one of those cases
else if (token.Equals('(') && (tokenChecker.IsNumber(topNewToken) || topNewToken.Equals(")") || topNewToken.Equals("x")))
{
newList.Add("*");
newList.Add(token.ToString());
}
else
{
newList.Add(token.ToString());
}
}
else
{
newList.Add(token.ToString());
}
}
// Those methods below can only be executed after adding
// symbol process is completed
CheckLastBlankNumber(ref newList);
CheckMultipleOperators(ref newList);
CheckUnary(ref newList);
return(newList);
}
/// <summary>
/// Parse infix to postfix using shunting yard algorithm
/// Source: https://en.wikipedia.org/wiki/Shunting-yard_algorithm
/// </summary>
public static List <string> ParseInfixToPostfix(List <string> tokenList)
{
TokenChecker tokenChecker = new TokenChecker();
Queue <string> outputQueue = new Queue <string>();
Stack <string> operatorStack = new Stack <string>();
// While there are tokens to be read
foreach (string token in tokenList)
{
string stringToken = token.ToString();
// If the token is a number, push it to the queue
if (tokenChecker.IsNumber(stringToken))
{
outputQueue.Enqueue(stringToken);
}
// If the token is 'x', push it to the stack
else if (stringToken.ToLower().Contains("x"))
{
operatorStack.Push(stringToken);
}
// If the token is an operator, do some logic by checking
// operator precedence
else if (tokenChecker.IsOperator(stringToken))
{
if (operatorStack.Count != 0)
{
string topOp = operatorStack.Peek();
while (topOp.ToLower().Contains("x") || (Operator.IsGreaterOp(topOp, stringToken)) && topOp != "(")
{
var currentOp = operatorStack.Pop();
outputQueue.Enqueue(currentOp);
if (operatorStack.Count != 0)
{
topOp = operatorStack.Peek();
}
else
{
break;
}
}
}
operatorStack.Push(stringToken);
}
// If the token is '(', push it to the stack
else if (token.Equals("("))
{
operatorStack.Push(stringToken);
}
// If the token is ')', push tokens in stack to the queue
// until the token from the stack equals '('
else if (token.Equals(")"))
{
var currentToken = operatorStack.Peek();
while (!currentToken.Equals("("))
{
var opToken = operatorStack.Pop();
outputQueue.Enqueue(opToken);
currentToken = operatorStack.Peek();
}
if (currentToken.Equals("("))
{
operatorStack.Pop();
}
}
}
// Push the rest tokens in the stack to the queue
while (operatorStack.Count != 0)
{
outputQueue.Enqueue(operatorStack.Pop());
}
List <string> postfixExp = new List <string>();
while (outputQueue.Any())
{
var val = outputQueue.Dequeue();
postfixExp.Add(val);
}
return(postfixExp);
}
