杭电_ACM_Wolf and Rabbit

本文通过一个趣味性的故事背景,深入探讨了寻找安全洞穴的问题,利用数学中的最大公约数(GCD)概念解决实际问题。详细解释了如何判断是否存在安全洞穴,并通过代码实现了解决方案。此过程不仅锻炼了读者的数学思维,还展示了算法在解决实际问题中的应用。
Problem Description
There is a hill with n holes around. The holes are signed from 0 to n-1.



A rabbit must hide in one of the holes. A wolf searches the rabbit in anticlockwise order. The first hole he get into is the one signed with 0. Then he will get into the hole every m holes. For example, m=2 and n=6, the wolf will get into the holes which are signed 0,2,4,0. If the rabbit hides in the hole which signed 1,3 or 5, she will survive. So we call these holes the safe holes.
 
Input
The input starts with a positive integer P which indicates the number of test cases. Then on the following P lines,each line consists 2 positive integer m and n(0<m,n<2147483648).
 
Output

            For each input m n, if safe holes exist, you should output "YES", else output "NO" in a single line.
 
Sample Input
2
1 2
2 2
 
Sample Output
NO
YES
View Code
 1 #include <stdio.h>
 2 //get the greatest common divisor
 3 int gcd(int a, int b)
 4 {
 5     int r;
 6     while (b)
 7     {
 8         r = a % b;
 9         a = b;
10         b = r;
11     }
12     return a;
13 }
14 int main()
15 {
16     int N, m, n;
17     scanf("%d", &N);
18     while(N--)
19     {
20         scanf("%d %d", &n, &m);
21         if(gcd(n, m) == 1)
22             printf("NO\n");
23         else
24             printf("YES\n");
25     }
26     return 0;
27 }

The reason why we can judge by greatest common divisor(gcd):

Condition:

firstly, r is the gcd of a, b and a is bigger than b, t is the lowest common multiple(lcm) of a, b

then you can get 

r = gcd(a, b)

t = a * b / r

secondly, the wolf find the t hold, the wolf will stop, because it's will be circulatory.

-------------------------

Question

the question is to find 0 < x < t / a and 0 < y < t / b to satisfy the equality

ax + r = by

for the equality, you will find (by - ax) / r is a integer, so you can find x, y making (by - ax) / r = 1

------------------------

Conclusion

"ax + r = by" means the r hole will be found, in other words, the gcd will be found.

so, if gcd is equal to 1, it means all holes will be found. if gcd is equal to other number, it means there are safe holes.

转载于:https://www.cnblogs.com/chuanlong/archive/2012/10/30/2745787.html

评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值