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LeetCode 3Sum

2024-08-03 17:07:46   217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)

 1 public class Solution { 2     public List<List<Integer>> threeSum(int[] num) { 3         HashSet<List<Integer>> set = new HashSet<List<Integer>>(); 4         int len=num.length; 5         Arrays.sort(num); 6         for (int i = 0; i < len-2; i++) { 7             if (num[i]>0)break; 8             for (int j = len-1 ; j >i+1 ; j--) { 9                 if (num[j]<0) break;10                 int ab = num[i] + num[j];11                 int c = -ab;12                 int k = bs(c, num, i + 1, j - 1);13                 if (k>0) {14                     ArrayList<Integer> list = new ArrayList<Integer>();15                     list.add(num[i]);16                     list.add(num[k]);17                     list.add(num[j]);18                     set.add(list);19                 }20             }21         }22         return new ArrayList<List<Integer>>(set);23     }24         int bs(int c, int[] num, int l, int r) {25         if(num[l] > c || num[r] < c) return -1;26         while(l <= r) {27             int m = (l+r)/2;28             if(num[m] == c) return m;29             else if(num[m] < c) l = m+1;30             else r = m-1;31         }32         return -1;33     }34 }

 

LeetCode 3Sum


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