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Light oj 1138 - Trailing Zeroes (III) 【二分查找好题】【 给出N!末尾有连续的Q个0,让你求最小的N】

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1138 - Trailing Zeroes (III)
Time Limit: 2 second(s) Memory Limit: 32 MB

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

Output for Sample Input

3

1

2

5

Case 1: 5

Case 2: 10

Case 3: impossible

 


PROBLEM SETTER: JANE ALAM JAN


题意:给你一个数Q,代表N!中   末尾连续0的个数。让你求出最小的N。


定理:求N!中  末尾连续0的个数

求法如下
LL sum(LL N)
{
    LL ans = 0;
    while(N)
    {
        ans += N / 5;
        N /= 5;
    }
    return ans;
}


本来不敢写,最后发现即使Q = 10^8也不会超long long(貌似int都不超)


又犯二了,区间开小了。WA了一次。



AC代码:用二分实现的


#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <queue>
#include <stack>
#include <vector>
#include <map>
#include <string>
#include <algorithm>
#define LL long long
#define MAXN 100+10
#define MAXM 20000+10
#define INF 0x3f3f3f3f
using namespace std;
LL sum(LL N)//求N阶乘中 末尾连续的0的个数
{
    LL ans = 0;
    while(N)
    {
        ans += N / 5;
        N /= 5;
    }
    return ans;
}
int k = 1;
int main()
{
    int t;
    LL Q;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%lld", &Q);
        LL left = 1, right = 1000000000000;//一开始开小了 醉了
        LL ans = 0;
        while(right >= left)
        {
            int mid = (left + right) >> 1;
            if(sum(mid) == Q)//相等时 要赋值给ans
            {
                ans = mid;
                right = mid - 1;
            }
            else if(sum(mid) > Q)
                right = mid - 1;
            else
                left = mid + 1;
        }
        printf("Case %d: ", k++);
        if(ans)
            printf("%lld\n", ans);
        else
            printf("impossible\n");
    }
    return 0;
}






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Light oj 1138 - Trailing Zeroes (III) 【二分查找好题】【 给出N!末尾有连续的Q个0,让你求最小的N】

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原文地址:http://blog.csdn.net/chenzhenyu123456/article/details/47812877

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