leetcode_c++:Divide and Conquer：Different Ways to Add Parentheses（241）

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]

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#include <bits/stdc++.h>using namespace std;const int N = 110;class Solution {private:    vector<int> dp[N][N];    vector<int> helper(string& input, int l, int r) {        if (!dp[l][r].empty())            return dp[l][r];        vector<int> &ans = dp[l][r];        bool isNum = true;        int num = 0;        for (int i = l; i < r; ++i) {            if (!isdigit(input[i])) {                isNum = false;                vector<int> L = helper(input, l, i), R = helper(input, i + 1, r);                for (auto l : L)                    for (auto r : R) {                        if (input[i] == '+') ans.push_back(l + r);                        else if (input[i] == '-') ans.push_back(l - r);                        else ans.push_back(l * r);                    }            }            if (isNum)                 num = num * 10 + (input[i] - '0');        }        if (isNum)            ans.push_back(num);        return ans;    }public:    vector<int> diffWaysToCompute(string input) {        return helper(input, 0, input.length());    }};int main() {    Solution s;    vector<int> ans;    // ans = s.diffWaysToCompute("0+1");    // for (auto i : ans) cout << i << ' ';    // cout << endl;    // ans = s.diffWaysToCompute("2-1-1");    // for (auto i : ans) cout << i << ' ';    // cout << endl;    ans = s.diffWaysToCompute("2*3-4*5");    for (auto i : ans) cout << i << ' ';    cout << endl;    return 0;}