leetcode 1 Two Sum

solution1:

class Solution {
public:
        struct pair{
                std::vector<int>* v;
                int i;

                bool operator < (const pair &a) const{
                        return (*v)[i] > (*a.v)[a.i];
                }
        };

    std::vector<int> twoSum(std::vector<int>& nums, int target) {
        std::vector<pair> nums2;
        std::vector<int> ret;
        sort(nums, nums2);
        int ns = nums.size();
        for(int i=0; i<ns-1; ++i){
                int tmp = target - nums[nums2[i].i];
                for(int j=i+1; j<ns; ++j){
                        if(tmp == nums[nums2[j].i]){
                                ret.push_back(nums2[i].i);
                                ret.push_back(nums2[j].i);
                                std::sort(ret.begin(), ret.end());
                                return ret;
                        }
                }
        }
        return ret;
    }

    void sort(std::vector<int>& nums, std::vector<pair>& nums2){
        int ns = nums.size();
        nums2.resize(ns);
        for(int i=0; i<ns; ++i){
                nums2[i].v = &nums;
                nums2[i].i = i;
        }

        std::sort(nums2.begin(), nums2.end());
    }
};

solution2:

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target){
        map <int, int> mp;
        vector <int> res(2);
        int n = nums.size();
        for (int i = 0; i < n; i++) {
            int another = target - nums[i];
            if (mp.count(another)) {
                res[0] = mp[another];
                res[1] = i;
                break;
            }
            mp[nums[i]] = i;
        }
        return res;
    }
};

两种方法思路大体相同，第二种更好，一方面使用了stl，代码简单明晰，另一方面，排序并不必要完全进行，利用map内部排序，使得一边排序一边查找，性能最佳。