BZOJ1671: [Usaco2005 Dec]Knights of Ni

 1 #include<cstdio>
 2 #include<cstring>
 3 struct target{
 4     int x,y;
 5 }t[1000001];
 6 struct queue{
 7     int x,y;
 8 }q[1000001];
 9 const int mx[4]={0,1,0,-1};
10 const int my[4]={1,0,-1,0};
11 int n,m,cnt,x1,y1,x2,y2,head,tail,ans=100000000;
12 int map[1001][1001];
13 int dis1[1001][1001];
14 int dis2[1001][1001];
15 bool mrk[1001][1001];
16 inline int min(int a,int b)
17 {return a<b?a:b;}
18 inline int read()
19 {
20     int x=0,f=1;char ch=getchar();
21     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
22     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}
23     return x*f;
24 }
25 inline void bfs1(int x,int y)
26 {
27     head=0;tail=1;mrk[x][y]=1;
28     q[1].x=x;q[1].y=y;
29     while (head<tail)
30     {
31         int nx=q[++head].x,ny=q[head].y;
32         for (int k=0;k<4;k++)
33           {
34               int xx=nx+mx[k],yy=ny+my[k];
35               if (xx<1||xx>n||yy<1||yy>m)continue;
36               if (mrk[xx][yy]||map[xx][yy]==1) continue;
37               dis1[xx][yy]=dis1[nx][ny]+1;
38               q[++tail].x=xx;q[tail].y=yy;
39               mrk[xx][yy]=1;
40           }
41     }
42 }
43 inline void bfs2(int x,int y)
44 {
45     memset(q,0,sizeof(q));
46     memset(mrk,0,sizeof(mrk));
47     head=0;tail=1;mrk[x][y]=1;
48     q[1].x=x;q[1].y=y;
49     while (head<tail)
50     {
51         int nx=q[++head].x,ny=q[head].y;
52         for (int k=0;k<4;k++)
53           {
54               int xx=nx+mx[k],yy=ny+my[k];
55               if (xx<1||xx>n||yy<1||yy>m)continue;
56               if (mrk[xx][yy]||map[xx][yy]==1) continue;
57               dis2[xx][yy]=dis2[nx][ny]+1;
58               q[++tail].x=xx;q[tail].y=yy;
59               mrk[xx][yy]=1;
60           }
61     }
62 }
63 int main()
64 {
65     m=read();n=read();
66     for (int i=1;i<=n;i++)
67       for(int j=1;j<=m;j++)
68       {
69         map[i][j]=read();
70         if (map[i][j]==4)
71         {
72             t[++cnt].x=i;
73             t[cnt].y=j;
74         }else
75         if (map[i][j]==2)
76         {
77             x1=i;
78             y1=j;
79             map[i][j]=0;
80         }else
81         if (map[i][j]==3)
82         {
83             x2=i;
84             y2=j;
85             map[i][j]=0;
86         }
87       }
88     bfs1(x1,y1);
89     bfs2(x2,y2);
90     for (int i=1;i<=cnt;i++)
91     {
92         int nx=t[i].x,ny=t[i].y;
93         if (!(dis1[nx][ny]+dis2[nx][ny]))continue;
94         ans=min(ans,dis1[nx][ny]+dis2[nx][ny]);
95     }
96     printf("%d",ans);
97 }