Question

Write a java class program to convert from

INFIX TO POSTFIX

Using stack operations

Answer 1

//Code Link => https://repl.it/@FAYAZPASHA/InnocentAgonizingQuote#Main.java

import java.util.Stack;

import java.util.*;

class Main

{

  

  static int Precdence(char ch) //returns the character priority

  {

    switch (ch)

    {

    case '+':

    case '-':

      return 1;

  

    case '*':

    case '/':

      return 2;

  

    case '^':

      return 3;

    }

    return -1;

  }

  

  static String infixToPostfix(String exp)

  {

    // initializing empty String for result

    String result = new String("");

    

    // initializing empty stack

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

    

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

    {

      char c = exp.charAt(i);

      

      // If the scanned character is an operand, add it to output.

      if (Character.isLetterOrDigit(c)) //if we encounter a operand we append to our results

        result += c;

      

    

      else if (c == '(') //if we encountered a opening parenthesis we push it to the stack

        stack.push(c);

      

      else if (c == ')') // when we encounter a closing parenthesis we check for the priority of the operator residing inside the stack

      {

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

          result += stack.pop();

        

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

          return "Invalid Expression"; // invalid expression        

        else

          stack.pop();

      }

      else // an operator is encountered

      {

        while (!stack.isEmpty() && Precdence(c) <= Precdence(stack.peek())){

          if(stack.peek() == '(')

            return "Invalid Expression";

          result += stack.pop();

      }

        stack.push(c);

      }

  

    }

  

    // pop all the operators from the stack

    while (!stack.isEmpty()){

      if(stack.peek() == '(')

        return "Invalid Expression";

      result += stack.pop();

    }

    return result;

  }

  

  // Driver method

  public static void main(String[] args)

  {

Scanner sc = new Scanner(System.in);

String exp = sc.nextLine();

    // String exp = "a+b*(c^d-e)^(f+g*h)-i";

    System.out.println(infixToPostfix(exp));

  }

}