Question

Convert infix to postfix

Answer 1

Answer:

static int checkSymbol(char ch)

{

switch (ch)

{

case '+':

case '-':

return 1;

case '*':

case '/':

return 2;

case '^':

return 3;

}

return -1;

}

static String convertInfixToPostfix(String expression)

{

String calculation = new String("");

Stack<Character> operands = new Stack<>();

Stack<Character> operators = new Stack<>();

 

for (int i = 0; i<expression.length(); ++i)

{

char c = expression.charAt(i);

if (Character.isLetterOrDigit(c))

operands.push(c);

else if (c == '(')

operators.push(c);

 

else if (c == ')')

{

while (!operators.isEmpty() && operators.peek() != '(')

operands.push(operators.pop());

 

if (!operators.isEmpty() && operators.peek() != '(')

return NULL;    

else

operators.pop();

}

else

{

while (!operators.isEmpty() && checkSymbol(c) <= checkSymbol(operators.peek()))

operands.push(operators.pop());

operators.push(c);

}

}

while (!operators.isEmpty())

operands.push(operators.pop());

while (!operands.isEmpty())

calculation+=operands.pop();

calculation=calculation.reverse();

return calculation;

}

Explanation:

• Create the checkSymbol function to see what symbol is being passed to the stack.
• Create the convertInfixToPostfix function that keeps track of the operands and the operators stack.
• Use conditional statements to check whether the character being passed is a letter, digit, symbol or a bracket.
• While the operators is  not empty, keep pushing the character to the operators stack.
• At last reverse and return the calculation which has all the results.