A ring is composed of n (even number) circles as shown in diagram. Put natural numbers 
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 <= 16)
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.
You are to write a program that completes above process.
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
很经典的深搜，启发
1，预处理非常重要，
（1），先求出所有的prime数最大 16+16，bool isprime[32],
（2）由于已经给出范围，我们可以先求出1-19的每个数下一个可能的取值，例如15，下一个可以取2,4,------两重for循环，可以避免搜索时重复判断。
2，用一个数组记录使输出的有序，op[n]与dfs(int begin,int n)中n对应
if( bp[t] )
{
op[o] = t ;
o ++ ;
bp[t] = false ;
dfs( t , n );//
o -- ;
bp[t] = true ;
}
posted on 2009-07-11 23:24
luis 阅读(296)
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