leetcode 3Sum

3sum.java

/*
Input: nums = [-1,0,1,2,-1,-4]
Output: [[-1,-1,2],[-1,0,1]]
*/
//if a+b+c=0 then output contains [a,b,c]
class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        
        //result that stores triplet
         List<List<Integer>> result= new ArrayList<>();
        
        //sort the arry, so duplicates will be placed next to each other
        Arrays.sort(nums);
        int length=nums.length;
        //iterate over the array till length-2 as we need 3 elements
        for(int i=0;i<length-2;i++){
            //ignore if element is same as the prev element
            if(i!=0 && nums[i]==nums[i-1]) continue;
            //two pointers
            int j=i+1;
            int k=nums.length-1;
            while(j<k){
                if(j!=i+1 && nums[j] == nums[j-1]){
                    j++;
                    continue;
                }
                if(k!=length-1 && nums[k]==nums[k+1]){
                    k--;
                    continue;
                }
                int sum=nums[i]+nums[j]+nums[k];
                if(sum==0){
                    result.add(Arrays.asList(nums[i],nums[j++],nums[k]));
                }
                else if(sum<0){
                    j++;
                }
                else{
                    k--;
                }
            }
        }
      return result;  
    }
}