往届 ACM 队训练题 (参考)

1005. Alex and Prime

单点时限: 2.0 sec

内存限制: 256 MB

When Kid came back, he was very tired. AK’s another member Alex would like to play with him, so gave him a problem about prime. You should help Kid, or he would never get time to rest.

A prime number is a number that is has no proper factors (it is only evenly divisible by 1 and itself). The first prime numbers are 2,3,5,7 but they quickly become less frequent. Adjacent primes are two numbers that are both primes, but there are no other prime numbers between the adjacent primes. For example, 2,3 are the only adjacent primes that are also adjacent numbers.

输入格式

The problem is like this: You are given 2 numbers: L and U (1<=L< U<=2,147,483,647 && U - L<=10000000 ), and you are to find the two adjacent primes C1 and C2 (L<=C1< C2<=U) that are closest (i.e. C2-C1 is the minimum).

输出格式

If there are other pairs that are the same distance apart, use the first pair. You are also to find the two adjacent primes D1 and D2 (L<=D1< D2<=U) where D1 and D2 are as distant from each other as possible (again choosing the first pair if there is a tie).

样例

Input
2 17
14 17
Output
2,3 are closest, 7,11 are most distant.
There are no adjacent primes.
不限期开放

题目列表