3Sum

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res=new ArrayList<>();
        if(nums.length<3 || nums==null) return res;
        Arrays.sort(nums);
        int k=nums.length-1;
        for(int i=0; i<nums.length; i++){
            int j=i+1;
            if(i>0 && nums[i]==nums[i-1]){
                continue;
            }
            while(j<k){
                if(k<nums.length-1 && nums[k]==nums[k+1]){
                    k--;
                    continue;
                }
                if(nums[i]+nums[j]+nums[k]>0){
                    k--;
                }
                else if(nums[i]+nums[j]+nums[k]<0){
                    j++;
                }
                else{
                    List<Integer> list=new ArrayList<>();
                    list.add(nums[i]);
                    list.add(nums[j]);
                    list.add(nums[k]);
               res.add(list);
                    k--;
                    j++;
                }
            }
            
        }
        return res;
    }
}

#Status: earnt about two pointer trick but could not solve the test case [-4,-2,-2,-2,0,1,2,2,2,3,3,4,4,6,6]
expected output for above:
[[-4,-2,6],[-4,0,4],[-4,1,3],[-4,2,2],[-2,-2,4],[-2,0,2]]
got [-4,-2,6],[-4,0,4],[-4,1,3],[-4,2,2]
have to use set for this.