You task is to find minimal natural number N, so that N! contains exactly Q zeroes on the trail in decimal notation. As you know N! = 1*2*...*N. For example, 5! = 120, 120 contains one zero on the trail.
Input
Input starts with an integer T (≤ 10000), denoting the number of test cases.
Each case contains an integer Q (1 ≤ Q ≤ 108) in a line.
Output
For each case, print the case number and N. If no solution is found then print 'impossible'.
Sample Input
3
1
2
5
Sample Output
Case 1: 5
Case 2: 10
Case 3: impossible
题解:零的个数可以来找5的因子个数。然后我们可以从1到1e8*5区间进行二分查找合适值。
#include<iostream>
using namespace std;
typedef long long ll;
ll f(ll x)
{
ll ans=0;
while(x)
{
ans+=x/5;
x/=5;
}
return ans;
}
ll halfsearch(int x)
{
int l=1,r=500000001,ans=0;
while(l<=r)
{
int mid=(l+r)/2;
if(f(mid)==x)
{
ans=mid;
r=mid-1;
}
else if(f(mid)<x)
l=mid+1;
else
r=mid-1;
}
return ans;
}
int main()
{
ll x;
int t;
cin>>t;
int k=1;
while(t--)
{
cin>>x;
int data=halfsearch(x);
cout<<"Case "<<k++<<":"<<" ";
if(data==0)
cout<<"impossible"<<endl;
else
cout<<data<<endl;
}
return 0;
}