LeetCode *** 241. Different Ways to Add Parentheses

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]

分析：

分治法。

代码：

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> first=diffWaysToCompute(input.substr(0,i));
vector<int> second=diffWaysToCompute(input.substr(i+1));

for(int f:first)
for(int s:second){
if(input[i]=='+')res.push_back(f+s);
else if(input[i]=='-')res.push_back(f-s);
else res.push_back(f*s);
}
}
}

if(res.empty())res.push_back(atoi(input.c_str()));
return res;
}
};