[U]Overfencing

簡單DP

/*ID:sevenst4;LANG:C++PROG:maze1*/#include<stdio.h>using namespace std;char m[222][88];int hi[101][40];int fx( int x ){ return (x<<1)-1; }int fy( int y ){ return (y<<1)-1; }int min( int a,int b ){ return a<b?a:b; } int main(){ freopen( "maze1.in","r",stdin ); freopen( "maze1.out","w",stdout ); int w,h; scanf( "%d %d",&w,&h ); char c; scanf( "%c",&c ); for( int i=0;i<2*h+1;i++ ) {  for( int j=0;j<2*w+1;j++ )    scanf( "%c",&m[i][j] );  scanf( "%c",&c );    }    int out[2][2];int cnt=0;for( int i=0;i<2*h+1;i++ ){ if( m[i][0]==' ' )      {   out[cnt][0]=i/2+1;   out[cnt][1]=1;   cnt++;     }     if( m[i][2*w]==' ' )      {   out[cnt][0]=i/2+1;   out[cnt][1]=w;   cnt++;     }    }        for( int j=0;j<2*w+1;j++ )    {  if( m[0][j]==' ' )  {    out[cnt][0]=1;   out[cnt][1]=j/2+1;   cnt++; }  if( m[2*h][j]==' ' )  {    out[cnt][0]=h;   out[cnt][1]=j/2+1;   cnt++; } }  for( int i=0;i<=h;i++ ) for( int j=0;j<=w;j++ )  hi[i][j]=111111; for( int i=0;i<cnt;i++ )  hi[out[i][0]][out[i][1]]=1; bool flag=true;while( flag ){   flag=false;  for( int i=1;i<=h;i++ )  for( int j=1;j<=w;j++ )      {    if( m[fx(i)][fy(j)-1]==' ' && hi[i][j]>hi[i][j-1]+1 )      hi[i][j]=hi[i][j-1]+1,flag=true;    if( m[fx(i)][fy(j)+1]==' ' && hi[i][j]>hi[i][j+1]+1 )      hi[i][j]=hi[i][j+1]+1,flag=true;    if( m[fx(i)-1][fy(j)]==' ' && hi[i][j]>hi[i-1][j]+1 )      hi[i][j]=hi[i-1][j]+1,flag=true;    if( m[fx(i)+1][fy(j)]==' ' && hi[i][j]>hi[i+1][j]+1 )      hi[i][j]=hi[i+1][j]+1,flag=true;      }}int max=0;for( int i=1;i<=h;i++ )for( int j=1;j<=w;j++ ) if( max<hi[i][j] )  max=hi[i][j];  printf( "%d\n",max );   return 0;}