| Time Limit: 5000MS | Memory Limit: 65536K | |
| Total Submissions: 5323 | Accepted: 2988 |
Description
The sequence of n − 1 consecutive composite numbers (positive integers that are not prime and not equal to 1) lying between two successive prime numbers p and p + n is called a prime gap of length n. For example, ‹24, 25, 26, 27, 28› between 23 and 29 is a prime gap of length 6.
Your mission is to write a program to calculate, for a given positive integer k, the length of the prime gap that contains k. For convenience, the length is considered 0 in case no prime gap contains k.
Input
The input is a sequence of lines each of which contains a single positive integer. Each positive integer is greater than 1 and less than or equal to the 100000th prime number, which is 1299709. The end of the input is indicated by a line containing a single zero.
Output
The output should be composed of lines each of which contains a single non-negative integer. It is the length of the prime gap that contains the corresponding positive integer in the input if it is a composite number, or 0 otherwise. No other characters should occur in the output.
Sample Input
10 11 27 2 492170 0
Sample Output
4 0 6 0 114
这道题就是一道数论的水题，先构造素数表，然后判断输入的n是否为素数，如果是素数的话，直接输出0，如果不是素数的话找到两个连续的素数，分别大于n和小于n输出这两个素数的差就可以了。。
代码：
语言：c++