Leetcode 18 三数之和

//双指针，不过因为是三个数所以左侧是两个下标


class Solution {
    public List> threeSum(int[] nums) {
        int n = nums.length;
        Arrays.sort(nums);
        List> ans = new ArrayList>();

        for(int i = 0; i < n; i++){
            if(i > 0 && nums[i] == nums[i - 1]) continue;
            int target = -nums[i];
            int k = n - 1;
            for(int j = i + 1; j < n; j++){
                if(j > i + 1 && nums[j] == nums[j - 1]) continue;
                while(j < k && nums[j] + nums[k] > target){
                    k--;
                }
                if(j == k) break;
                if(nums[j] + nums[k] == target){
                    List tmp = new ArrayList<>();
                    tmp.add(nums[i]);
                    tmp.add(nums[j]);
                    tmp.add(nums[k]);
                    ans.add(tmp);
                }
            }
        }
        return ans;
    }
}