problem:
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:
For example, given array S = {-1 0 1 2 -1 -4},
A solution set is:
(-1, 0, 1)
(-1, -1, 2)
Solution: 先排序 然后左右夹逼 时间复杂度：O(n2)
class Solution {
public:
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> result;
if(nums.size()<3) return result;
//先排序 然后再左右夹逼
sort(nums.begin(),nums.end());
const int target=0;
auto last=nums.end();
for(auto a=nums.begin();a<prev(last,2);a++)
{
auto b = next(a);
auto c= prev(last);
while(b<c)
{
if(*a+*b+*c<target)
b++;
else if(*a+*b+*c>target)
--c;
else{
result.push_back({*a,*b,*c});
++b;
--c;
}
}
}
return result;
}
};
原文：http://www.cnblogs.com/xiaoying1245970347/p/4552498.html