# HDU 1016 Prime Ring Problem C语言版

HDU题解 3736浏览

Description

A ring is compose of n circles as shown in diagram. Put natural number 1, 2, …, n into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

Note: the number of first circle should always be 1.

Input

n (0 < n < 20). Output

The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements. Print solutions in lexicographical order.

You are to write a program that completes above process.

Print a blank line after each case.

Sample Input

6
8

Sample Output

Case 1:
1 4 3 2 5 6
1 6 5 2 3 4

Case 2:
1 2 3 8 5 6 7 4
1 2 5 8 3 4 7 6
1 4 7 6 5 8 3 2
1 6 7 4 3 8 5 2

Slyar:大意是给出N，求所有由1-N组成的首位为1环形序列，要求相邻两数的和为素数。素数判断不说了，因为N小于20，所以可以预先将素数打表保存供后面查询。因为规定了首位为1，所以从1开始搜索所有的可能，用visit[]标记访问过的数字，每次搜到深度等于N的时候就可以打印结果path[]了。没有结果的也就空着输出就好了，格式方面注意每行结果的最后一个数字后面没有空格。

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