POJ1753 BFS+位运算

题意：翻转某些牌 使得达到目标状态

BFS+位运算

因为整个图比较小，所以用位运算来记录状态。

View Code

 1 #include<stdio.h>

 2 #include<stdlib.h>

 3 #include<string.h>

 4 #include<queue>

 5 using namespace std;

 6 const int inf = 0x7fffffff;

 7 const int maxn = 16;

 8 const int maxm = 65535;

 9 int vis[ maxm+5 ];

10 int dis[ maxm+5 ];

11 int mat[ maxn ][ maxn ];

12 int bina[]={1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768};

13 int cc[16]={19,39,78,140,305,626,1252,2248,4880,10016,20032,35968,12544,29184,58368,51200};

14 int main( int argc,char argv[] ){

15     char a[ maxn ];

16     int sum=0;

17     for( int i=0;i<4;i++ ){

18         scanf("%s",a);

19         for( int j=0;j<4;j++ ){

20             if( a[j]=='b' ){

21                 mat[i][j]=1;

22             }

23             else{

24                 mat[i][j]=0;

25             }

26             sum+=(bina[4*i+j]*mat[i][j]);

27         }

28     }

29     memset( vis,0,sizeof(vis) );

30     for( int i=0;i<=maxm;i++ )

31         dis[ i ]=inf;

32     if( sum==0||sum==maxm ){

33         vis[ sum ]=1;

34         dis[ sum ]=0;

35     }

36     queue<int>q;

37     vis[ sum ]=1;

38     dis[ sum ]=0;

39     q.push( sum );

40     while( !q.empty() ){

41         int now=q.front();

42         q.pop();

43         if( now==0||now==maxm ){

44             vis[ now ]=1;

45             break;

46         }

47         if( vis[0]||vis[ maxm ] ){

48             break;

49         }

50         for( int i=0;i<16;i++ ){

51             int next=now^cc[i];

52             if( vis[ next ]==0 ){

53                 vis[ next ]=1;

54                 dis[ next ]=dis[ now ]+1;

55                 q.push( next );

56             }

57             else{

58                 if( dis[ next ]>dis[ now ]+1 ){

59                     dis[ next ]=dis[ now ]+1;

60                 }

61             }

62         }

63     }

64     if( vis[ 0 ]==1 ||vis[ maxm ]==1 ){

65         printf("%d\n",min( dis[0],dis[ maxm ] ) );

66     }

67     else

68     {

69           printf("Impossible\n");

70     }

71     return 0;

72 }