Classic 150 Interview Questions P150: Evaluate Reverse Polish Notation

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Timeline

Timeline

2025-11-19

init

Stack

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Problem:

P150 Evaluate Reverse Polish Notation

https://leetcode.cn/problems/evaluate-reverse-polish-notation/description/?envType=study-plan-v2&envId=top-interview-150

Classic problem. Here, since the problem guarantees the reverse Polish expression is valid, no validation is performed.

#include <string>
#include <vector>
#include <stack>

using std::vector;
using std::string;
using std::stack;

class Solution {
    public:
	int evalRPN(vector<string> &tokens)
	{
		stack<int> st;
		int val1, val2, res = 0;
		for (string &token : tokens) {
			if (!token.compare("+") || !token.compare("-") || !token.compare("*") || !token.compare("/")) {
				val1 = st.top();
				st.pop();
				val2 = st.top();
				st.pop();
				if (!token.compare("+"))
					st.push(val2 + val1);
				else if (!token.compare("-"))
					st.push(val2 - val1);
				else if (!token.compare("*"))
					st.push(val2 * val1);
				else if (!token.compare("/"))
					st.push(val2 / val1);
			} else {
				st.push(std::stoi(token));
			}
		}
		return st.top();
	}
};