分析
注意hash去重
class Solution {
public:
/**
* @param numbers : Give an array numbers of n integer
* @return : Find all unique triplets in the array which gives the sum of zero.
*/
vector<vector<int> > threeSum(vector<int> &nums) {
// write your code here
vector<vector<int>> ret;
unordered_set<long long> d;
for (int i = 0; i < nums.size() - 2; ++i) {
int sum = -nums[i];
unordered_set<int> s;
for (int j = i + 1; j < nums.size(); ++j) {
if (s.find(nums[j]) != s.end()) {
vector<int> ans;
ans.push_back(nums[i]);
ans.push_back(nums[j]);
ans.push_back(-(nums[i] + nums[j]));
sort(ans.begin(), ans.end());
long long t = 33 * 33 * ans[0] + 33 * ans[1] + ans[2];
if (d.find(t) == d.end()) {
ret.push_back(ans);
d.insert(t);
}
} else {
s.insert(sum - nums[j]);
}
}
}
return ret;
}
};
