下面 count_triple 函数的时间复杂度为( )。
1 int count_triple(int n) {
2 int cnt = 0;
3 for (int a = 1; a <= n; a++)
4 for (int b = a; a + b <= n; b++) {
5 int c = sqrt(a * a + b * b);
6 if (a + b + c > n)
7 break;
8 if (a * a + b * b == c * c)
9 cnt++;
10 }
11 return cnt;
12 }
O(n)
O(n2)
O(n3)
O(n4)