3Sum.java

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        Arrays.sort(nums);
        int a = nums.length;
        int l,r;
        List<List<Integer>> twoDList = new ArrayList<>();
        for(int i=0; i<a-2; i++){
            if(i>0 && nums[i]==nums[i-1]) continue;
            l = i+1;
            r = a-1;
            while(l < r){
                int sum = nums[i] + nums[l] + nums[r];
                if(sum == 0){
                    List<Integer> oneDList = new ArrayList<>();
                    oneDList.add(nums[i]);
                    oneDList.add(nums[l]);
                    oneDList.add(nums[r]);
                    twoDList.add(oneDList);
                    l++; r--;
                    while(l<r && nums[l]==nums[l-1]) l++;
                    while(l<r && nums[r]==nums[r+1]) r--;
                }
                else if(sum<0){
                    l++;
                }
                else{
                    r--;
                }
            }
        }
        return twoDList;
    }
}