LeetCode----241. Different Ways to Add Parenthese(M)分治

1 题目

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)) = 2

Output: [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) = 10

Output: [-34, -14, -10, -10, 10]

2 分析和实现

      用分治思想实现

class Solution {public:    vector<int> diffWaysToCompute(string input) {                vector<int> res;                for(int i = 0; i < input.size(); i++) {            char cur = input[i];                        if(cur == '+' || cur == '-' || cur == '*') {                vector<int> res_left = diffWaysToCompute(input.substr(0, i));                vector<int> res_right = diffWaysToCompute(input.substr(i + 1));                 for(int x = 0; x < res_left.size(); x++) {                    for(int y = 0; y < res_right.size(); y++) {                        if(cur == '+')                            res.push_back(res_left[x] + res_right[y]);                        else if(cur == '-')                            res.push_back(res_left[x] - res_right[y]);                        else if(cur == '*')                            res.push_back(res_left[x] * res_right[y]);                    }                }            }        }                //单独一个数字时        if(res.empty()) {            res.push_back(atoi(input.c_str()));        }                return res;       }};