暴力搜索：
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
vector<int> v(2);
for(int i = 0; i < nums.size(); i ++) {
for(int j = i + 1; j < nums.size(); j ++) {
if(nums[i] + nums[j] == target) {
v[0] = i;
v[1] = j;
return v;
}
}
}
}
};