3Sum

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

class Solution {
  public List<List<Integer>> threeSum(int[] num) {
        Arrays.sort(num);
        List<List<Integer>> lists = new ArrayList<>();
        for (int i = 0; i < num.length - 2; i++) {
            int lo = i + 1;
            int lh = num.length - 1;
            if (i == 0 || (i > 0 && num[i] != num[i - 1])) {
                while (lo < lh) {
                    if (num[i] + num[lo] + num[lh] == 0) {
                        lists.add(Arrays.asList(num[i], num[lo], num[lh]));
                        while (lo < lh && num[lo] == num[lo + 1]) lo++;
                        while (lo < lh && num[lh] == num[lh - 1]) lh--;
                        lo++;
                        lh--;
                      
                    } else {
                        if (num[lo] + num[lh] < -num[i]) {
                            lo++;
                        } else {
                            lh--;
                        }
                    }

                }
            }

        }
        return lists;


    }
}