#18四数之和

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

final class Solution {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums);
        int n = nums.length;
        for (int first = 0; first + 3 < n; first++) {
            if (first > 0 && nums[first] == nums[first - 1]) continue;
            for (int second = first + 1; second + 2 < n; second++) {
                if (second > first + 1 && nums[second] == nums[second - 1]) continue;
                long remaining = (long) target - nums[first] - nums[second];
                int left = second + 1;
                int right = n - 1;
                while (left < right) {
                    long pair = (long) nums[left] + nums[right];
                    if (pair < remaining) {
                        left++;
                    } else if (pair > remaining) {
                        right--;
                    } else {
                        result.add(List.of(nums[first], nums[second], nums[left], nums[right]));
                        int leftValue = nums[left];
                        int rightValue = nums[right];
                        while (left < right && nums[left] == leftValue) left++;
                        while (left < right && nums[right] == rightValue) right--;
                    }
                }
            }
        }
        return result;
    }
}