leetcode个人题解——#18 4sums

在3sums的基础上加了一层循环。

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        vector<vector<int>> ans;
        if (nums.size() < ) return ans;
        for(unsigned int j = ;j < nums.size() - ; j++)
        {
            if ((j>) && (nums[j]==nums[j-]))
                 continue;
            for (unsigned int i = j+; i < nums.size()-; i++)
            {
                 int l = i+;
                 int r = nums.size() - ;
                 while(l < r)
                 {
                    int sum = nums[i] + nums[l] + nums[r] + nums[j];
                    if (sum > target) r--;
                    else if (sum < target) l++;
                    else if (sum == target)
                    {
                        ans.push_back(vector<int>{nums[j], nums[i],nums[l],nums[r]});
                        while(l<r && nums[l] == nums[l+])l++;
                        while(l<r && nums[r] == nums[r-])r--;
                        l++;
                        r--;
                    }
                }
                while(nums[i] == nums[i+] && i<nums.size() -) i++;
            }
        }
        return ans;
    }
};