leetcode15 three sum

import java.util.*;
class Solution {
    public List<List<Integer>> threeSum(int[] sum) {
         List<List<Integer>> result=new LinkedList<>();   
    if (sum==null||sum.length<3) {
        return result;
    }
    Arrays.sort(sum);//sort
    int len=sum.length;
    for(int i=0;i<len-2;i++){
        if(i>0&&sum[i]==sum[i-1]){
            continue;
        }
        int left=i+1;
        int right=len-1;
        while(left<right){
            int res=sum[i]+sum[left]+sum[right];
            if (res>0) {
                right--;
            }else if (res<0) {
                left++;
            }else{
                result.add(Arrays.asList(sum[i],sum[left],sum[right])); 
                while(left<right&&sum[left]==sum[left+1]){
                    left++;
                }
                while(left<right&&sum[right]==sum[right-1]){
                    right--;
                }
                left++;
                right--;  
            }
            
            
        }
    }
    return result;
    }
}