BZOJ-4808: 马 (二分图最大独立集 WAing~)

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 typedef long long LL;
 4 const int MAX=1005;
 5 int n,m,a[MAX][MAX],id[MAX][MAX],b[MAX][MAX],tx,ans;
 6 int fa[MAX*MAX];
 7 bool vis[MAX*MAX];
 8 int dx[8]={-2,-1,1,2,2,1,-1,-2};
 9 int dy[8]={1,2,2,1,-1,-2,-2,-1};
10 int dfs(int x){
11     int i,j;
12     for (i=1;i<=tx;i++)
13         if (!vis[i] && b[x][i]){
14             vis[i]=true;
15             if (fa[i]==-1 || dfs(fa[i]))
16                 return fa[i]=x,1;
17         }
18     return 0;
19 }
20 int main(){
21     freopen ("horse.in","r",stdin);freopen ("horse.out","w",stdout);
22     int i,j,k,x,y;
23     scanf("%d%d",&n,&m);
24     for (i=1;i<=n;i++)
25         for (j=1;j<=m;j++)
26             scanf("%d",&a[i][j]),id[i][j]=a[i][j]==0?++tx:0;
27     for (i=1;i<=n;i++)
28         for (j=1;j<=m;j++)
29             if (!a[i][j])
30                 for (k=0;k<8;k++){
31                     x=i+dx[k],y=j+dy[k];
32                     if (x<1 || x>n || y<1 || y>m || a[x][y]) continue;
33                     b[ id[i][j] ][ id[x][y] ]=1;
34                 }
35     memset(fa,-1,sizeof(fa));
36     int zt=0;
37     for (i=1;i<=tx;i++){
38         memset(vis,false,sizeof(vis));
39         zt+=dfs(i);
40     }
41     printf("%d",tx-zt/2);
42     return 0;
43 }