#4354. [GESP202506 八级 C++] 第 11 题

[GESP202506 八级 C++] 第 11 题

下面 count_triple 函数的时间复杂度为( )。

int gcd(int a, int b) {
    if (a == 0)
        return b;
    return gcd(b % a, a);
}
int count_triple(int n) {
    int cnt = 0;
    for (int v = 1; v * v * 4 <= n; v++)
        for (int u = v + 1; u * (u + v) * 2 <= n; u += 2)
            if (gcd(u, v) == 1) {
                int a = u * u - v * v;
                int b = u * v * 2;
                int c = u * u + v * v;
                cnt += n / (a + b + c);
            }
    return cnt;
}

{{ select(1) }}

  • O(n)O(n)
  • O(n2)O(n^2)
  • O(nlogn)O(n \log n)
  • O(n2logn)O(n^2 \log n)