playground/leetcode/150-evaluate-reverse-polish-notation/150-evaluate-reverse-polish-notation.cpp at main · MuhtasimTanmoy/playground · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
class Solution {
public:
    int evalRPN(vector<string>& tokens) {

        function<int(string)> toInt = [](string s) -> int {
            int res = 0;
            for(auto c: s) {
                if (c == '-') continue;
                res = res * 10; res += (c - '0');
            }
            return s[0] == '-' ? -res: res;
        };

        stack<int> args;
        unordered_set<char> operations = {'+', '-', '*', '/'};

        for(auto token: tokens) {

            if (token.size() == 1 && operations.count(token[0])) {

                auto secondArg = args.top(); args.pop();
                auto firstArg = args.top(); args.pop();

                int res = 0;

                switch (token[0]) {
                    case '+':
                        res = firstArg + secondArg;
                        break;
                    case '-':
                        res = firstArg - secondArg;
                        break;
                    case '*':
                        res = firstArg * secondArg;
                        break;
                    case '/':
                        res = firstArg / secondArg;
                }

                args.push(res);

            } else args.push(toInt(token));
        }

        return args.top();
    }
};