leetcode 15 三数之和 解题笔记 排序+双指针

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        if (nums == null || nums.length == 0) {
            return res;
        }
        Arrays.sort(nums);
        for (int first = 0; first < nums.length; first++) {
            if (first > 0 && nums[first] == nums[first-1]) {
                continue;
            }
            int target = -nums[first];
            int second = first + 1;
            int third = nums.length - 1;
            while (second < third) {
                if (second > first + 1 && nums[second] == nums[second-1]) {
                    second++;
                    continue;
                }
                if (nums[second] + nums[third] == target) {
                    List<Integer> list = new ArrayList<>();
                    list.add(nums[first]);
                    list.add(nums[second]);
                    list.add(nums[third]);
                    res.add(list);
                    second++;
                } else if (nums[second] + nums[third] < target) {
                    second++;
                } else {
                    third--;
                }

            }
        }
        return res;
    }
}