241. Different Ways to Add Parentheses 添加括号的不同方式

[GH1995]

241. Different Ways to Add Parentheses

Difficulty: Medium

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

Example 2:

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

Solution

Language: C++

class Solution {
public:
    vector<int> diffWaysToCompute(string input) {
      vector<int> res;
​
      for (int i = 0; i < input.size(); ++i) {
        if (input[i] == '+' || input[i] == '-' || input[i] == '*') {
          vector<int> left = diffWaysToCompute(input.substr(0, i));
          vector<int> right = diffWaysToCompute(input.substr(i + 1));
​
          for (int j = 0; j < left.size(); ++j)
            for (int k = 0; k < right.size(); ++k) {
              if (input[i] == '+')
                res.push_back(left[j] + right[k]);
              else if (input[i] == '-')
                res.push_back(left[j] - right[k]);
              else if (input[i] == '*')
                res.push_back(left[j] * right[k]);
            }
        }
      }
​
      if (res.empty())
        res.push_back(stoi(input));
      return res;
    }
};