LeetCode 15. 三数之和(3Sum)

15. 三数之和
15. 3Sum

题目描述
Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note: The solution set must not contain duplicate triplets.

LeetCode15. 3Sum中等

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]

]

Java 实现

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        if (nums == null || nums.length < 3) {
            return res;
        }
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            if (i == 0 || nums[i] > nums[i - 1]) {
                int j = i + 1;
                int k = nums.length - 1;
                while (j < k) {
                    if (nums[i] + nums[j] + nums[k] == 0) {
                        List<Integer> list = new ArrayList<>();
                        list.add(nums[i]);
                        list.add(nums[j]);
                        list.add(nums[k]);
                        res.add(list);
                        j++;
                        k--;
                        while (j < k && nums[j] == nums[j - 1]) {
                            j++;
                        }
                        while (j < k && nums[k] == nums[k + 1]) {
                            k--;
                        }
                    } else if (nums[i] + nums[j] + nums[k] < 0) {
                        j++;
                    } else {
                        k--;
                    }
                }
            }
        }
        return res;
    }

    public static void main(String[] args) {
        int[] nums = {-1, 0, 1, 2, -1, -4};
        System.out.println(new Solution().threeSum(nums));
    }
}

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参考资料