Java/Others/StackPostfixNotation.java at master · primary-code-test/Java · GitHub

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package Others;

import java.util.*;

public class StackPostfixNotation {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

String post = scanner.nextLine(); // Takes input with spaces in between eg. "1 21 +"

System.out.println(postfixEvaluate(post));

scanner.close();

}

// Evaluates the given postfix expression string and returns the result.

public static int postfixEvaluate(String exp) {

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

Scanner tokens = new Scanner(exp);

while (tokens.hasNext()) {

if (tokens.hasNextInt()) {

s.push(tokens.nextInt()); // If int then push to stack

} else { // else pop top two values and perform the operation

int num2 = s.pop();

int num1 = s.pop();

String op = tokens.next();

if (op.equals("+")) {

s.push(num1 + num2);

} else if (op.equals("-")) {

s.push(num1 - num2);

} else if (op.equals("*")) {

s.push(num1 * num2);

} else {

s.push(num1 / num2);

}

// "+", "-", "*", "/"

}

tokens.close();

return s.pop();

}