LightOJ - 1138 Trailing Zeroes (III) 二分

//
#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll search(ll n){
	ll ans =0;
	while(n>0){
		ans+=(n/5);
		n/=5;
	}
	return ans;
}
int main()
{
	ll n,t,cnt=1;
	ll l,r,mid,ans;
	scanf("%lld",&t);
	while(t--){
		scanf("%lld",&n);
		l = 1,r = 1e9;ans = 0;
		while(l<=r){
			mid = (l+r)>>1;
			if(search(mid)==n){
				ans = mid;
				r = mid - 1;
			}
			else if(search(mid)<n)
			l = mid+1;
			else r = mid-1;
		}
		printf("Case %lld: ",cnt++);
		if(ans>0)
		printf("%lld\n",ans);
		else printf("impossible\n");
	}
	return 0;
}