[LeetCode] 241. Different Ways to Add Parentheses

Given a string of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. The valid operators are +, - and *.

Example 1
Input: “2-1-1”.

((2-1)-1) = 0(2-(1-1)) = 2Output: [0, 2]

Example 2

Input: "2*3-4*5"(2*(3-(4*5))) = -34((2*3)-(4*5)) = -14((2*(3-4))*5) = -10(2*((3-4)*5)) = -10(((2*3)-4)*5) = 10Output: [-34, -14, -10, -10, 10]

class Solution {public:    vector<int> diffWaysToCompute(string input) {        return diffWaysToCompute(input, 0, (int)input.size() - 1);    }private:    vector<int> diffWaysToCompute(string input, int start, int end) {        vector<int> vec;        for (int i = start + 1; i < end; i++) {            if (input[i] != '+' && input[i] != '-' && input[i] != '*')                continue;            auto lops = diffWaysToCompute(input, start, i - 1);            auto rops = diffWaysToCompute(input, i + 1, end);            for (auto lop : lops) {                for (auto rop : rops) {                    int res;                    switch (input[i]) {                        case '+':                            res = lop + rop;                            break;                        case '-':                            res = lop - rop;                            break;                        case '*':                            res = lop * rop;                            break;                        default:                            break;                    }                    vec.push_back(res);                }            }        }        if (vec.empty())            vec.push_back(stoi(input.substr(start, end - start + 1)));        return vec;    }};