HDU2553 （N皇后+DFS）

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 1 #include<stdio.h>

 2 #include<string.h>

 3 #include<stdlib.h>

 4 #include<queue>

 5 using namespace std;

 6 const int maxn = 21;

 7 const int inf = INT_MAX;

 8 int r[ maxn ],c[ maxn ],sd[ maxn ],md[ maxn ];//sd=r+c,md=r-c+n-1;

 9 int ans,n;

10 void init(){

11     memset( r,0,sizeof( r ));

12     memset( c,0,sizeof( c ));

13     memset( sd,0,sizeof( sd ));

14     memset( md,0,sizeof( md ));

15     ans=0;

16 }

17 

18 void dfs( int x,int y,int sum ){

19     if( sum==n ) {

20         ans++;

21         return ;

22     }

23     for( int i=x;i<n;i++ ){

24         for( int j=0;j<n;j++ ){

25             if( r[ i ]==1||c[ j ]==1||sd[ i+j ]==1||md[ i-j+n-1 ]==1 ) continue;

26             r[ i ]=c[ j ]=sd[ i+j ]=md[ i-j+n-1 ]=1;

27             dfs( i,j,sum+1 );

28             r[ i ]=c[ j ]=sd[ i+j ]=md[ i-j+n-1 ]=0;

29         }

30     }

31 }

32 

33 int main(){

34     int aa[12]={0};

35     aa[10]=724;

36     while( scanf("%d",&n)==1 && n ){

37         if( aa[n]!=0 ){

38             printf("%d\n",aa[n]);

39             continue;

40         }

41         init();

42         dfs( 0,0,0 );//x,y,sum

43         aa[n]=ans;

44         printf("%d\n",aa[n]);

45     }

46     return 0;

47 }