Leetcode-[2] evaluate reverse Polish notation

Evaluate reverse Polish notation total accepted: 24595Total submissions: 123794My submissions

 

Evaluate the value of an arithmetic expression in reverse Polish notation.

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

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

 

 

Idea: simple application of stack

#include <iostream>#include <vector>#include <string>#include <stack>#include <cstdlib>using namespace std;class Solution {public:    int evalRPN(vector<string> &tokens) {        stack<int> s;        string str;        int a, b;        for (int i = 0; i < tokens.size(); i++) {            str = tokens[i];            if (str == "+" || str == "-" || str == "*" ||                 a = s.top(); s.pop();                b = s.top(); s.pop();                switch(str[0]) {                    case ‘+‘: s.push(b+a); break;                    case ‘-‘: s.push(b-a); break;                    case ‘*‘: s.push(b*a); break;                    case ‘/‘: s.push(b/a); break;                    }            }            else {                s.push(atoi(str.c_str()));            }        }        a = s.top();s.pop();        return a;    }};int main(int argc, char *argv[]) {    Solution* solution = new Solution();    vector<string> tokens;    tokens.push_back("2");    tokens.push_back("1");    tokens.push_back("+");    tokens.push_back("3");    tokens.push_back("*");    cout << solution->evalRPN(tokens) << endl;    vector<string> tokens2;    tokens2.push_back("4");    tokens2.push_back("13");    tokens2.push_back("5");    tokens2.push_back("/");    tokens2.push_back("+");    cout << solution->evalRPN(tokens2) << endl;    return 0;}

 

Leetcode-[2] evaluate reverse Polish notation