3sum.java

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {

        List<List<Integer>> result = new ArrayList<>();
        if(nums.length<3) return result;

        Arrays.sort(nums);
        for(int i=0; i+2<nums.length; i++){
            if(i>0 && nums[i] == nums[i-1])
                continue;
            int j=i+1, k=nums.length - 1;
            int target = -nums[i];
            while(j<k){
                if(nums[j]+nums[k] == target){
                    result.add(Arrays.asList(nums[i],nums[j],nums[k]));
                    j++; k--;
                    while(j<k && nums[j] == nums[j-1]) j++;
                    while(j<k && nums[k] == nums[k+1]) k--;
                }
                else if(nums[j]+nums[k] > target) k--;
                else j++;
            }
        }
        return result;
    }
}