package stack_and_queue;

// Problem Title => Java program to evaluate value of a postfix expression

import java.util.*;

import java.util.Stack;

public class P12 {

// Method to evaluate value of a postfix expression

static int evaluatePostfix(String exp) {

//create a stack

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

// Scan all characters one by one

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

char c = exp.charAt(i);

// If the scanned character is an operand (number here), push it to the stack.

if(Character.isDigit(c))

stack.push(c - '0');

// If the scanned character is an operator, pop two elements from stack apply the operator

else {

int val1 = stack.pop();

int val2 = stack.pop();

switch(c) {

case '+':

stack.push(val2+val1);

break;

case '-':

stack.push(val2- val1);

break;

case '/':

stack.push(val2/val1);

break;

case '*':

stack.push(val2*val1);

break;

}

}

}

return stack.pop();

}

// Driver program to test above functions

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

String exp = sc.nextLine();

sc.close();

// String exp="231*+9-";

System.out.println("postfix evaluation: "+evaluatePostfix(exp));

}

}