双指针算法：四数之和解题思路与实现

知识点概览

三数之和参考代码

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        int n = nums.size();
        sort(nums.begin(), nums.end());
        vector<vector<int>> ret;
        for (int i = 0; i < n; ) {
            int left = i + 1;
            int right = n - 1;
            int target = -nums[i];
            if (nums[i] > 0) break;
            while (left < right) {
                int s = nums[left] + nums[right];
                if (s < target) left++;
                else if (s > target) right--;
                else {
                    ret.push_back({nums[i], nums[left], nums[right]});
                    left++;
                    right--;
                    while (left < right && nums[left] == nums[left - 1]) left++;
                    while (left < right && nums[right] == nums[right + 1]) right--;
                }
            }
            i++;
            while (i < n && nums[i] == nums[i - ]) i++;
        }
         ret;
    }
};