XDU1019 阶乘因子的个数

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>

using namespace std;
typedef long long LL;
int M;

int check(LL mid)   //mid 的阶乘中5的个数
{
    LL a = 5;
    int res = 0;
    while(a <= mid)
    {
        res += mid/a;
        a *= 5;
    }
    return res;
}

int main()
{
    int T;
    cin>>T;
    while(T--)
    {
        cin>>M;
        LL l=1, r=1000000000;
        LL res = -1;
        while(l <= r)
        {
            LL mid = (l+r)/2;
            int tp = check(mid);
            if(tp == M)
            {
                res = mid;
                r = mid-1;
            }
            else if(tp > M) r = mid - 1;
            else l = mid + 1;
        }
        if(res == -1)
            cout<<"No solution\n";
        else
            cout<<res<<endl;
    }
    return 0;
}