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[Leetcode] 3Sum

2024-07-30 13:08:02   218人阅读

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:

  • Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
  • The solution set must not contain duplicate triplets.

 

    For example, given array S = {-1 0 1 2 -1 -4},    A solution set is:    (-1, 0, 1)    (-1, -1, 2)

 

Solution:

 1 public class Solution { 2     public List<List<Integer>> threeSum(int[] num) { 3         List<List<Integer>> result = new ArrayList<List<Integer>>(); 4         if (num.length < 3) 5             return result; 6         Arrays.sort(num); 7         for (int i = 0; i < num.length - 2; ++i) { 8             if (i > 0 && num[i] == num[i - 1]) 9                 continue;10             int a = num[i];11             int low = i + 1;12             int high = num.length - 1;13             while (low < high) {14                 if (-a == num[low] + num[high]) {15                     List<Integer> temp = new ArrayList<Integer>();16                     temp.add(a);17                     temp.add(num[low]);18                     temp.add(num[high]);19                     result.add(temp);20                     low++;21                     high--;22                     while (low < high && num[low] == num[low - 1])23                         low++;24                     while (low < high && num[high] == num[high + 1])25                         high--;26                 } else if (-a > num[low] + num[high])27                     low++;28                 else29                     high--;30             }31         }32         return result;33     }34 }

注意：如果current value=http://www.mamicode.com/=previous value，需要跳过当前值。

[Leetcode] 3Sum


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