HDU-1016 Prime Ring Problem DFS

　　简单DFS，需要注意的是最后的那个数加上一要是个素数。

　　代码如下：

#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
using namespace std;int hash[25], rec[25], cnt;bool isprime( int x )
{if( x<= 1 ) return false;if( x== 2 ) return true;int lim= sqrt( x );for( int i= 2; i<= lim; ++i ){if( x% i== 0 ) return false;}return true;
}void DFS( int last, int cnt, int N )
{if( cnt== N ){if( isprime( rec[N- 1]+ 1 ) ){for( int i= 0; i< cnt; ++i ){printf( i== 0? "%d": " %d", rec[i] );}puts( "" );}return;}for( int i= 1; i<= N; ++i ){if( !hash[i]&& isprime( last+ i ) ){rec[cnt]= i;hash[i]= 1;DFS( i, cnt+ 1, N );hash[i]= 0;}}
}int main()
{int N, ca= 0;while( scanf( "%d", &N )!= EOF ){rec[0]= 1;hash[1]= 1;printf( "Case %d:\n", ++ca );DFS( 1, 1, N );puts( "" );}return 0;
}

转载于:https://www.cnblogs.com/Lyush/archive/2011/08/11/2135494.html

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