2022.07.22 _ a day

15. 三数之和

题目描述

给你一个包含 n 个整数的数组 nums,判断 nums 中是否存在三个元素 a,b,c ,使得 a + b + c = 0 ？请你找出所有和为 0 且不重复的三元组.

注意：答案中不可以包含重复的三元组.

示例 1：

输入：nums = [-1,0,1,2,-1,-4]
输出：[[-1,-1,2],[-1,0,1]]

示例 2：

输入：nums = []
输出：[]

示例 3：

输入：nums = [0]
输出：[]

提示：

• 0 <= nums.length <= 3000
• -105 <= nums[i] <= 105

Related Topics

• 数组
• 双指针
• 排序

coding

// May heaven not need to be heavy、、、
class Solution {
    
    public List<List<Integer>> threeSum(int[] nums) {
    
        List<List<Integer>> res = new ArrayList<>();
        if (nums.length < 3) {
    
            return res;
        }
        Arrays.sort(nums);
        for (int first = 0; first < nums.length; first ++) {
    
            if (nums[first] > 0) {
    
                break;
            }
            if (first > 0 && nums[first] == nums[first - 1]) {
    
                continue;
            }
            int second = first + 1;
            int third = nums.length - 1;
            while (second < third) {
    
                if (nums[second] + nums[first] + nums[third] == 0) {
    
                    res.add(Arrays.asList(new Integer[]{
    nums[first], nums[second], nums[third]}));
                    while (second < third && nums[second] == nums[second + 1]) {
    
                        second ++;
                    }
                    while (second < third && nums[third] == nums[third - 1]) {
    
                        third --;
                    }
                    second ++;
                    third --;
                }else if (nums[second] + nums[first] + nums[third] < 0) {
    
                    second ++;
                } else {
    
                    third --;
                }
            }
        }
        return res;
    }
}