Evaluate Reverse Polish Notation – LeetCode Solution Java , Python 3, Python 2 , C , C++, Best and Optimal Solutions , All you need.

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, and /. Each operand may be an integer or another expression.

Note that division between two integers should truncate toward zero.

It is guaranteed that the given RPN expression is always valid. That means the expression would always evaluate to a result, and there will not be any division by zero operation.

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

Constraints:

• 1 <= tokens.length <= 104
• tokens[i] is either an operator: "+", "-", "*", or "/", or an integer in the range [-200, 200].

C++ Evaluate Reverse Polish Notation LeetCode Solution

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();
    }
};

Java Evaluate Reverse Polish Notation LeetCode Solution

import java.util.Stack;

public class Solution {
    public int evalRPN(String[] tokens) {
        int a,b;
		Stack<Integer> S = new Stack<Integer>();
		for (String s : tokens) {
			if(s.equals("+")) {
				S.add(S.pop()+S.pop());
			}
			else if(s.equals("/")) {
				b = S.pop();
				a = S.pop();
				S.add(a / b);
			}
			else if(s.equals("*")) {
				S.add(S.pop() * S.pop());
			}
			else if(s.equals("-")) {
				b = S.pop();
				a = S.pop();
				S.add(a - b);
			}
			else {
				S.add(Integer.parseInt(s));
			}
		}	
		return S.pop();
	}
}
 

Python 3 Evaluate Reverse Polish Notation LeetCode Solution

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()

Array-1180
String-562
Hash Table-412
Dynamic Programming-390
Math-368
Sorting-264
Greedy-257
Depth-First Search-256
Database-215
Breadth-First Search-200
Tree-195
Binary Search-191
Matrix-176
Binary Tree-160
Two Pointers-151
Bit Manipulation-140
Stack-133
Heap (Priority Queue)-117
Design-116
Graph-108
Simulation-103
Prefix Sum-96
Backtracking-92
Counting-86
Sliding Window-73
Linked List-69
Union Find-66
Ordered Set-48
Monotonic Stack-47
Recursion-43
Trie-41
Binary Search Tree-40
Divide and Conquer-40
Enumeration-39
Bitmask-37
Queue-33
Memoization-32
Topological Sort-31
Geometry-30
Segment Tree-27
Game Theory-24
Hash Function-24
Binary Indexed Tree-21
Interactive-18
Data Stream-17
String Matching-17
Rolling Hash-17
Shortest Path-16
Number Theory-16
Combinatorics-15
Randomized-12
Monotonic Queue-9
Iterator-9
Merge Sort-9
Concurrency-9
Doubly-Linked List-8
Brainteaser-8
Probability and Statistics-7
Quickselect-7
Bucket Sort-6
Suffix Array-6
Minimum Spanning Tree-5
Counting Sort-5
Shell-4
Line Sweep-4
Reservoir Sampling-4
Eulerian Circuit-3
Radix Sort-3
Strongly Connected Componen-t2
Rejection Sampling-2
Biconnected Component-1

Leave a comment below

Related posts:

Next Permutation – LeetCode Solution Sudoku Solver – LeetCode Solution Insert Interval – LeetCode Solution Search a 2D Matrix – LeetCode Solution Subsets II – LeetCode Solution Surrounded Regions – LeetCode Solution