[itint5]三数和为0

#include <algorithm>
using namespace std;
typedef tuple<int, int, int> ABC; //存放a,b,c三元组

//返回所有满足条件的(a,b,c)三元组
vector<ABC> threeSumZero(vector<int> &arr) {
vector<ABC> ans;
sort(arr.begin(), arr.end());
int k = 0;
while (k < arr.size()) {
int i = k+1;
int j = arr.size() - 1;
while (i < j) {
if (arr[i] + arr[j] == -arr[k]) {
ans.push_back(make_tuple(arr[k], arr[i], arr[j]));
while (i+1 < arr.size() && arr[i] == arr[i+1]) i++;
while (j-1 >= 0 && arr[j-1] == arr[j]) j++;
i++;
j--;
} else if (arr[i] + arr[j] < -arr[k]) {
i++;
} else {
j--;
}
}
while (k+1 < arr.size() && arr[k] == arr[k+1]) k++;
k++;
}
return ans;
}