组合0

 

#include <iostream>
using namespace std;

// 计算n的阶乘中质因数p的个数
int countFactor(int n, int p) {
    int count = 0;
    while (n) {
        n /= p;
        count += n;
    }
    return count;
}

int main() {
    int t;
    cin >> t;
    while (t--) {
        int n, m;
        cin >> n;
        cin >> m;
        // 计算组合数C(n, m)中质因数5的个数与质因数2的个数的较小值
        int twoCount = countFactor(n, 2) - countFactor(m, 2) - countFactor(n - m, 2);
        int fiveCount = countFactor(n, 5) - countFactor(m, 5) - countFactor(n - m, 5);
        cout << min(twoCount, fiveCount) << endl;
    }
    //10只能由2和5贡献，看谁多
    //就像挑人组队一样，谁少取决于谁
    return 0;
}