Here, We see Evaluate Reverse Polish Notation LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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Evaluate Reverse Polish Notation LeetCode Solution

Problem Statement

You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation.

Evaluate the expression. Return an integer that represents the value of the expression.

Note that:

• The valid operators are ‘+’, ‘-‘, ‘*’, and ‘/’.
• Each operand may be an integer or another expression.
• The division between two integers always truncates toward zero.
• There will not be any division by zero.
• The input represents a valid arithmetic expression in a reverse polish notation.
• The answer and all the intermediate calculations can be represented in a 32-bit integer.

Example 1:
Input: tokens = [“2″,”1″,”+”,”3″,”*”]
Output: 9
Explanation: ((2 + 1) * 3) = 9

Example 2:
Input: tokens = [“4″,”13″,”5″,”/”,”+”]
Output: 6
Explanation: (4 + (13 / 5)) = 6

Example 3:
Input: tokens = [“10″,”6″,”9″,”3″,”+”,”-11″,”*”,”/”,”*”,”17″,”+”,”5″,”+”]
Output: 22
Explanation:
((10 * (6 / ((9 + 3) * -11))) + 17) + 5
= ((10 * (6 / (12 * -11))) + 17) + 5
= ((10 * (6 / -132)) + 17) + 5
= ((10 * 0) + 17) + 5
= (0 + 17) + 5
= 17 + 5
= 22

Evaluate Reverse Polish Notation LeetCode Solution C++

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        unordered_map<string, function<int (int, int) > > map = {
            { "+" , [] (int a, int b) { return a + b; } },
            { "-" , [] (int a, int b) { return a - b; } },
            { "*" , [] (int a, int b) { return a * b; } },
            { "/" , [] (int a, int b) { return a / b; } }
        };
        std::stack<int> stack;
        for (string& s : tokens) {
            if (!map.count(s)) {
                stack.push(stoi(s));
            } else {
                int op1 = stack.top();
                stack.pop();
                int op2 = stack.top();
                stack.pop();
                stack.push(map[s](op2, op1));
            }
        }
        return stack.top();
    }
};Code language: PHP (php)

Evaluate Reverse Polish Notation LeetCode Solution Java

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Long> stack = new Stack<>();
        int n = tokens.length;
        for (int i = 0; i < n; i++) {
            if (tokens[i].length() == 1 && tokens[i].charAt(0) < 48) {
                long integer2 = stack.pop();
                long integer1 = stack.pop();
                char operator = tokens[i].charAt(0);
                long resolvedAns = resolves(integer1, integer2, operator);
                stack.push(resolvedAns);
            } else {
                stack.push(Long.parseLong(tokens[i]));
            }
        }
        return stack.pop().intValue();        
    }
    long resolves(long a, long b, char Operator) {
        if (Operator == '+') return a + b;
        else if (Operator == '-') return a - b;
        else if (Operator == '*') return a * b;
        return a / b;
    }
}Code language: JavaScript (javascript)

Evaluate Reverse Polish Notation Solution JavaScript

var evalRPN = function(tokens) {
  let stack = [];
  let ops = {
    '+': (a, b) => a + b,
    '-': (a, b) => a - b,
    '*': (a, b) => a * b,
    '/': (a, b) => a / b >= 0 ? Math.floor(a / b) : Math.ceil(a / b),
  };
  for (let t of tokens) {
    if (ops[t]) {
      let top = stack.pop();
      let second = stack.pop();
      stack.push(ops[t](second, top));
    } else {
      stack.push(Number(t));
    }
  }
  return stack.pop();    
};Code language: JavaScript (javascript)

Evaluate Reverse Polish Notation Solution Python

class Solution(object):
    def evalRPN(self, tokens):
        stack = []
        for t in tokens:
            if t not in "+-*/":
                stack.append(int(t))
            else:
                r, l = stack.pop(), stack.pop()
                if t == "+":
                    stack.append(l+r)
                elif t == "-":
                    stack.append(l-r)
                elif t == "*":
                    stack.append(l*r)
                else:
                    stack.append(int(float(l)/r))
        return stack.pop()