[LeetCode] 15. 3Sum

传送门

Description

Given an array S of n integers, are there elements a, b, c in S 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.

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For example, given array S = [-1, 0, 1, 2, -1, -4],   A solution set is: [   [-1, 0, 1],   [-1, -1, 2] ]

思路

题意：给出一串整数值，输出a + b + c = 0的方案

题解：求三个数之和为0的方案则可以转换成求两个数为0的方案。

 

+ View Code?

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public class Solution {     //72ms     public List<List<Integer>> threeSum(int[] nums) {         List<List<Integer>>res = new ArrayList<>();         int len = nums.length;         Arrays.sort(nums);         for (int i = 0;i < len - 2;i++){             int sum = -nums[i];             int left = i + 1,right = len - 1;             while (left < right){                 if (nums[left] + nums[right] < sum){                     left++;                 } else if (nums[left] + nums[right] > sum){                     right--;                 } else{                     res.add(Arrays.asList(nums[i],nums[left],nums[right]));                     while (++left < right && nums[left] == nums[left - 1]){}                     while (--right > left && nums[right] == nums[right + 1]){}                 }             }             while (i + 1 < len - 2 && nums[i + 1] == nums[i]){                 i++;             }         }         return res;     }   }