暴力搜索一下, 时间复杂度 O( 小于 n^2)

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target) {
        vector<int>vec;
        for ( int i = 0; i < numbers.size(); i++ ) {
            for ( int j = i + 1; j < numbers.size(); j++ ) {
                if ( numbers[i] + numbers[j] == target) {
                    vec.push_back(i + 1);
                    vec.push_back(j + 1);
                    break;
                }
            }
        }
        return vec;
    }
};