prblm15.java

import java.util.*;

public class prblm15 {
    public static void main(String[] args) {
        int[] nums = {-1,0,1,2,-1,-4};
        System.out.println(threeSum(nums));
    }
    public static List<List<Integer>> threeSum(int[] nums) {
        Arrays.sort(nums);
        List<List<Integer>> ans = new ArrayList<>();
        int n = nums.length;
        for (int i = 0; i < n - 2 && nums[i] <= 0; ++i) {
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            int j = i + 1;
            int k = n - 1;
            while (j < k) {
                int x = nums[i] + nums[j] + nums[k];
                if (x < 0) {
                    j++;
                } else if (x > 0) {
                    k--;
                } else {
                    ans.add(List.of(nums[i], nums[j++], nums[k--]));
                    while (j < k && nums[j] == nums[j - 1]) {
                        j++;
                    }
                    while (j < k && nums[k] == nums[k + 1]) {
                        k--;
                    }
                }
            }
        }
        return ans;
    }
}