CasperT CasperT - 1 month ago 24
C# Question

infix to postfix converter

I have been working on this infix to postfix/polis notation converter.
Although, I do not feel the solution is adequate.
Specifically the j (EDIT: Now called index) variable is bugging me.

Do you guys have any suggestions? Or perhaps there is a much better way to accomplish it? Or do I just worry too much?

public static string[] InfixToPostfix(string[] infixArray)
{
var stack = new Stack<string>();
var postfix = new string[infixArray.Length];

int index = 0;
string st;
for (int i = 0; i < infixArray.Length; i++)
{
if (!(MyMath.MathOperators.Contains(infixArray[i])))
{
postfix[index] = infixArray[i];
index++;
}
else
{
if (infixArray[i].Equals("("))
{
stack.Push("(");
}
else if (infixArray[i].Equals(")"))
{
st = stack.Pop();
while (!(st.Equals("(")))
{
postfix[index] = st;
index++;
st = stack.Pop();
}
}
else
{
while (stack.Count > 0)
{
st = stack.Pop();
if (RegnePrioritet(st) >= RegnePrioritet(infixArray[i]))
{
postfix[index] = st;
index++;
}
else
{
stack.Push(st);
break;
}
}
stack.Push(infixArray[i]);
}
}
}
while (stack.Count > 0)
{
postfix[index] = stack.Pop();
index++;
}

return postfix.TakeWhile(item => item != null).ToArray();
}

Answer

If you replace array by a Stack<string>, you don't have to keep track where you are with the index variable.

You can then return your result with postfixStack.ToArray()

My implementation:

public static string[] InfixToPostfix( string[] infixArray )
{
    var stack = new Stack<string>();
    var postfix = new Stack<string>();

    string st;
    for ( int i = 0 ; i < infixArray.Length ; i++ )
    {
        if ( !( "()*/+-".Contains( infixArray[ i ] ) ) )
        {
            postfix.Push(infixArray[i]);
        }
        else
        {
            if ( infixArray[ i ].Equals( "(" ) )
            {
                stack.Push( "(" );
            }
            else if ( infixArray[ i ].Equals( ")" ) )
            {
                st = stack.Pop();
                while ( !( st.Equals( "(" ) ) )
                {
                    postfix.Push( st );
                    st = stack.Pop();
                }
            }
            else
            {
                while ( stack.Count > 0 )
                {
                    st = stack.Pop();
                    if ( RegnePrioritet( st ) >= RegnePrioritet( infixArray[ i ] ) )
                    {
                        postfix.Push(st);
                    }
                    else
                    {
                        stack.Push( st );
                        break;
                    }
                }
                stack.Push( infixArray[ i ] );
            }
        }
    }
    while ( stack.Count > 0 )
    {
        postfix.Push(stack.Pop());
    }

    return postfix.Reverse().ToArray();
}