basic-calculator.cc

#include "leetcode.h"

using namespace std;

class Solution {
  public:
    int calculate(const string &str) {
        size_t idx = 0;
        return calculate(str, idx);
    }

    int calculate(const string &str, size_t &idx) const {
        int64_t res = 0;
        for (char opr = '+'; idx < str.size();) {
            switch (str[idx]) {
                case '+':
                case '-': opr = str[idx++]; break;
                case '(':
                    ++idx;
                    res += opr == '+' ? calculate(str, idx) : -calculate(str, idx);
                    break;
                case ')': ++idx; return res;
                default:
                    if (isdigit(str[idx])) {
                        int64_t x = str[idx++] - '0';
                        while (idx < str.size() && isdigit(str[idx])) { x = x * 10 + str[idx++] - '0'; }
                        res += opr == '+' ? x : -x;
                    } else {
                        ++idx;
                    }
                    break;
            }
        }
        return res;
    }
};

int main(int argc, char const *argv[]) {
    Solution solution;
    cout << solution.calculate("1-(2-(3-2))") << endl;         // 0
    cout << solution.calculate("1 + 1") << endl;               // 2
    cout << solution.calculate(" 2-1 + 2 ") << endl;           // 3
    cout << solution.calculate("(1+(4+5+2)-3)+(6+8)") << endl; // 23
}