Leetcode#18 4Sum

class Solution {
    public:
        vector<vector<int>> fourSum(vector<int>& nums, int target) {
            vector<vector<int>> res;

            if(nums.size() < 4)
                return res;

            sort(nums.begin(), nums.end());

            for(int i=0; i<nums.size(); i++) {
                if (i > 0 && nums[i] == nums[i-1])
                    continue;

                int tmp = target - nums[i];

                for(int j=i+1; j<nums.size(); j++) {
                    if (j > i+1 && nums[j] == nums[j-1])
                        continue;

                    int left = j+1;
                    int right = nums.size()-1;
                    int tmp2 = tmp-nums[j];

                    while (left < right) {
                        if (tmp2 == nums[left] + nums[right]) {
                            vector<int> ans;
                            ans.push_back(nums[i]);
                            ans.push_back(nums[j]);
                            ans.push_back(nums[left]);
                            ans.push_back(nums[right]);
                            res.push_back(ans);

                            left++;
                            while(left < nums.size() && nums[left] == nums[left-1]) left++;

                            right--;
                            while(right >=0 && nums[right] == nums[right+1]) right--;
                        } else if (tmp2 > nums[left] + nums[right]) {
                            left++;
                        } else {
                            right--;
                        }
                    }        
                }
            }
            return res;
        }
};