Medium
过两天面Yelp, k sum在最近面经里频率还行，拿来做做吧。还是处理edge case的时候卡了一下, 记一下内部的while循环要记得加上bound: left < right, 顺便再记一下这个api:

Arrays.asList(nums[i], nums[l], nums[r])

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