3Sum

public class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        Arrays.sort(nums);
        int i = 0;
        while(i < nums.length && nums[i] <= 0){
            int high = nums.length-1;
            int low = i + 1;
            while(nums[high] >= 0 && low < high){
                if((nums[low] + nums[high] + nums[i]) < 0){
                    low++;
                }else if((nums[low] + nums[high] + nums[i]) > 0){
                    high--;
                }else{
                    List<Integer> list = new ArrayList<Integer>();
                    list.add(nums[i]);
                    list.add(nums[low]);
                    list.add(nums[high]);
                    res.add(list);
                    low++;
                    while(low < high && nums[low] == nums[low-1]){
                          low++;
                    }
                    
                }
            }
            i++;
            while(i < nums.length && nums[i] == nums[i-1]){
                i++;
            }
        }
        return res;
    }
}
// solution from 2Sum
public List<List<Integer>> threeSum(int[] num) {
    Arrays.sort(num);
    List<List<Integer>> res = new LinkedList<>(); 
    for (int i = 0; i < num.length-2; i++) {
        if (i == 0 || (i > 0 && num[i] != num[i-1])) {
            int lo = i+1, hi = num.length-1, sum = 0 - num[i];
            while (lo < hi) {
                if (num[lo] + num[hi] == sum) {
                    res.add(Arrays.asList(num[i], num[lo], num[hi]));
                    while (lo < hi && num[lo] == num[lo+1]) lo++;
                    while (lo < hi && num[hi] == num[hi-1]) hi--;
                    lo++; hi--;
                } else if (num[lo] + num[hi] < sum) lo++;
                else hi--;
           }
        }
    }
    return res;
}