19.1.29 [LeetCode 18] 4Sum

Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note:

The solution set must not contain duplicate quadruplets.

Example:

Given array nums = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:
[
  [-1,  0, 0, 1],
  [-2, -1, 1, 2],
  [-2,  0, 0, 2]
]

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        int size = nums.size();
        sort(nums.begin(), nums.end());
        vector<vector<int>> ans;
        for (int i = 0; i < size; i++) {
            if (i > 0 && nums[i] == nums[i - 1])continue;
            for (int j = i + 1; j < size - 2; j++) {
                if (j > i + 1 && nums[j] == nums[j - 1])continue;
                int p = j + 1, q = size - 1;
                int res = target - nums[i] - nums[j];
                while (p < q) {
                    int tmp = nums[p] + nums[q];
                    if (tmp < res)p++;
                    else if (tmp == res) {
                        vector<int> tt;
                        tt.push_back(nums[i]);
                        tt.push_back(nums[j]);
                        tt.push_back(nums[p]);
                        tt.push_back(nums[q]);
                        ans.push_back(tt);
                        while (nums[p + 1] == nums[p])p++;
                        while (nums[q - 1] == nums[q])q--;
                        p++, q--;
                    }
                    else q--;
                }
            }
        }
        return ans;
    }
};

跟3sum基本相同