[bzoj2638] 黑白染色

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 const int maxn=2523,xx[4]={1,-1,0,0},yy[4]={0,0,1,-1};
 7 struct zs{
 8     int too,pre;
 9 }e[123333];int tot,last[maxn];
10 struct zs1{int x,y;}dl[maxn];
11 char mp[53][53];
12 int id[53][53];
13 int col[maxn],d[maxn];
14 short dis[maxn];
15 bool u[maxn];
16 int i,j,k,n,m,ans,cnt;
17  
18 int ra;char rx;
19 inline int read(){
20     rx=getchar(),ra=0;
21     while(rx<‘0‘||rx>‘9‘)rx=getchar();
22     while(rx>=‘0‘&&rx<=‘9‘)ra*=10,ra+=rx-48,rx=getchar();return ra;
23 }
24 inline void insert(int a,int b){
25 //  printf("%d-->%d\n",a,b);
26     e[++tot].too=b,e[tot].pre=last[a],last[a]=tot,
27     e[++tot].too=a,e[tot].pre=last[b],last[b]=tot;
28 }
29  
30 int main(){
31     n=read(),m=read();
32     for(i=1;i<=n;i++)scanf("%s",mp[i]+1);
33     for(i=1;i<=n;i++)for(j=1;j<=m;j++)if(!id[i][j]){
34         int l=0,r=1,nx,ny,x,y;dl[1]=(zs1){i,j};
35         cnt++,col[cnt]=mp[i][j]==‘B‘,id[i][j]=cnt;
36         while(l<r){
37             l++,nx=dl[l].x,ny=dl[l].y;
38             for(k=0;k<4;k++){
39                 x=nx+xx[k],y=ny+yy[k];
40                 if(x<1||y<1||x>n||y>m)continue;
41                 if(mp[x][y]==mp[i][j]&&!id[x][y])
42                     dl[++r]=(zs1){x,y},id[x][y]=cnt;
43                 else if(id[x][y])insert(id[x][y],cnt);
44             }
45         }
46     }
47     ans=1e9;
48     for(i=1;i<=cnt;i++){
49         memset(dis,0,(cnt+1)<<1);
50         int l=0,r=1,now,j;d[1]=i,dis[i]=1;
51         while(l<r)
52             for(j=last[now=d[++l]];j;j=e[j].pre)if(!dis[e[j].too])
53                 dis[e[j].too]=dis[now]+1,d[++r]=e[j].too;
54         ans=min(ans,dis[d[r]]-(!col[d[r]]));
55     }
56     printf("%d\n",ans);
57 }