原图中相邻点两两连边，容量为1，源点连接狼的节点，容量为INF，羊的节点连接汇点，容量为INF，这样求最小割就可以了。
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;
#define maxn 50000
#define INF 100000
struct Edge
{
int from, to, cap, flow;
};
int s, t;
vector<Edge> edges; // 边数的两倍
vector<int> G[maxn]; // 邻接表，G[i][j]表示结点i的第j条边在e数组中的序号
bool vis[maxn]; // BFS使用
int d[maxn]; // 从起点到i的距离
int cur[maxn]; // 当前弧指针
int map[210][210];
int sum[210][210];
int min(int a,int b)
{
if(a<b) return a;
else return b;
}
void AddEdge(int from, int to, int cap)
{
int len;
Edge temp;
temp.from=from;temp.to=to;temp.cap=cap;temp.flow=0;
edges.push_back(temp);
temp.from=to;temp.to=from;temp.cap=0;temp.flow=0;
edges.push_back(temp);
len = edges.size();
G[from].push_back(len-2);
G[to].push_back(len-1);
}
bool BFS()
{
memset(vis, 0, sizeof(vis));
queue<int> Q;
Q.push(s);
vis[s] = 1;
d[s] = 0;
while(!Q.empty())
{
int x = Q.front(); Q.pop();
for(int i = 0; i < G[x].size(); i++)
{
Edge& e = edges[G[x][i]];
if(!vis[e.to] && e.cap > e.flow)
{
vis[e.to] = 1;
d[e.to] = d[x] + 1;
Q.push(e.to);
}
}
}
return vis[t];
}
int DFS(int x, int a)
{
if(x == t || a == 0) return a;
int flow = 0, f;
for(int& i = cur[x]; i < G[x].size(); i++)
{
Edge& e = edges[G[x][i]];
if(d[x] + 1 == d[e.to] && (f = DFS(e.to, min(a, e.cap-e.flow))) > 0)
{
e.flow += f;
edges[G[x][i]^1].flow -= f;
flow += f;
a -= f;
if(a == 0) break;
}
}
return flow;
}
int Maxflow()
{
int flow = 0;
while(BFS())
{
memset(cur, 0, sizeof(cur));
flow += DFS(s, INF);
}
return flow;
}
int main()
{
int row,col;
int i,j;
int cas=0;
while(scanf("%d%d",&row,&col)!=EOF)
{
cas++;
int tot=0;
memset(map,0,sizeof(0));
memset(sum,0,sizeof(0));
s=0;t=row*col+1;
for(i=0;i<=t+10;i++) G[i].clear();
for(i=1;i<=row;i++)
for(j=1;j<=col;j++)
{
tot++;
sum[i][j]=tot;
}
for(i=1;i<=row;i++)
for(j=1;j<=col;j++)
{
scanf("%d",&map[i][j]);
if(j+1<=col)
{
AddEdge(sum[i][j],sum[i][j+1],1);
AddEdge(sum[i][j+1],sum[i][j],1);
}
if(i+1<=row)
{
AddEdge(sum[i][j],sum[i+1][j],1);
AddEdge(sum[i+1][j],sum[i][j],1);
}
if(map[i][j]==1)
AddEdge(sum[i][j],t,INF);
else if(map[i][j]==2)
AddEdge(s,sum[i][j],INF);
}
printf("Case %d:
",cas);
printf("%d
",Maxflow());
}
}