3Sum
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)
- 排序
- 夹逼定理
-
避免重复
class Solution { public: vector<vector<int>> threeSum(vector<int>& nums) { vector<vector<int>> res; if(!nums.size()){ return res; } sort(nums.begin(), nums.end()); auto begin = nums.begin(); auto last = nums.end(); for(auto i=begin; i<prev(last,2) && *i<=0; i++){ if(i!=begin && *i==*(i-1)){ continue; } auto j=i+1; auto k=last-1; while(j<k){ auto t = *i+*j+*k; if(t==0){ res.push_back({*i,*j,*k}); j++; k--; while(j<k && *j==*(j-1)){ j++; } while(j<k && *(k+1)==*k){ k--; } } else if(t<0){ j++; } else if(t>0){ k--; } } } return res; } };
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