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我自己的建图方式，然后wa了，这样建图错误的原因是会有重边：
然后不死心，想着标记一下边，尝试后发现，标到反边我就糊涂了；
附上错误代码
#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cctype>
#include <vector>
#include <queue>
using namespace std;
const int N = 20100;
const int INF = 0x3f3f3f3f;
struct edge
{
int to, cap, next;
} g[N*100];
int level[N], iter[N], head[N], que[N];
int n, m, cnt;
int a[N],b[N];
int vis[1000][1000];
int bis[1000][1000];
void add_edge(int v, int u, int cap)
{
g[cnt].to = u, g[cnt].cap = cap, g[cnt].next = head[v], head[v] = cnt++;
g[cnt].to = v, g[cnt].cap = 0, g[cnt].next = head[u], head[u] = cnt++;
}
bool bfs(int s, int t)
{
memset(level, -1, sizeof level);
level[s] = 0;
int st = 0, en = 0;
que[0] = s;
while(st <= en)
{
int v = que[st++];
for(int i = head[v]; i != -1; i = g[i].next)
{
int u = g[i].to;
if(g[i].cap > 0 && level[u] < 0)
{
level[u] = level[v] + 1;
que[++en] = u;
}
}
}
return level[t] == -1;
}
int dfs(int v, int t, int f)
{
if(v == t) return f;
int tm = f;
for(int &i = iter[v]; i != -1; i = g[i].next)
{
int u = g[i].to;
if(g[i].cap > 0 && level[v] < level[u])
{
int d = dfs(u, t, min(tm, g[i].cap));
g[i].cap -= d, g[i^1].cap += d, tm -= d;
if(tm == 0) break;
}
}
if(tm == f) level[v] = -1;
return f - tm;
}
int dinic(int s, int t)
{
int flow = 0, f;
while(true)
{
if(bfs(s, t)) return flow;
memcpy(iter, head, sizeof head);
flow += dfs(s, t, INF);
}
}
int main()
{
int f,d;
while(~scanf("%d%d%d",&n,&f,&d))
{
cnt=0;
memset(head, -1, sizeof head);
memset(vis,0,sizeof(vis));
memset(bis,-1,sizeof(bis));
int s=0,t=n+f+d+1;
for(int i=1; i<=n; i++)
{
add_edge(s,i,1); //起点和牛
int f1,d1;
scanf("%d%d",&f1,&d1);
for(int j=1; j<=f1; j++)
{
scanf("%d",&a[j]);
add_edge(i,a[j]+n,1);//牛和饭
}
for(int j=1; j<=d1; j++)
{
scanf("%d",&b[j]);
add_edge(b[j]+n+f,t,1);//菜和终点
}
for(int i=1; i<f1; i++)
{
for(int j=1; j<=d1; j++)
{
if(vis[a[i]+n][b[j]+n+f]==0&&bis[b[j]+n+f][a[i]+n]==-1)
{
add_edge(a[i]+n,b[j]+n+f,1);
vis[a[i]+n][b[j]+n+f]=1; //饭和菜
bis[b[j]+n+f][a[i]+n]=0;
}
}
}
}
printf("%d\n", dinic(0, t));
}
}
正确的建图方式：拆点，将牛拆出一个副本，让牛1和牛11的容量为1，其他的如图所示，这样避免了重边：
正确代码：
#include <iostream>
#include <string>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cctype>
#include <vector>
#include <queue>
using namespace std;
const int N = 20100;
const int INF = 0x3f3f3f3f;
struct edge
{
int to, cap, next;
} g[N*100];
int level[N], iter[N], head[N], que[N];
int n, m, cnt;
int a[N],b[N];
void add_edge(int v, int u, int cap)
{
g[cnt].to = u, g[cnt].cap = cap, g[cnt].next = head[v], head[v] = cnt++;
g[cnt].to = v, g[cnt].cap = 0, g[cnt].next = head[u], head[u] = cnt++;
}
bool bfs(int s, int t)
{
memset(level, -1, sizeof (level));
level[s] = 0;
int st = 0, en = 0;
que[0] = s;
while(st <= en)
{
int v = que[st++];
for(int i = head[v]; i != -1; i = g[i].next)
{
int u = g[i].to;
if(g[i].cap > 0 && level[u] < 0)
{
level[u] = level[v] + 1;
que[++en] = u;
}
}
}
return level[t] == -1;
}
int dfs(int v, int t, int f)
{
if(v == t) return f;
int tm = f;
for(int &i = iter[v]; i != -1; i = g[i].next)
{
int u = g[i].to;
if(g[i].cap > 0 && level[v] < level[u])
{
int d = dfs(u, t, min(tm, g[i].cap));
g[i].cap -= d, g[i^1].cap += d, tm -= d;
if(tm == 0) break;
}
}
if(tm == f) level[v] = -1;
return f - tm;
}
int dinic(int s, int t)
{
int flow = 0, f;
while(true)
{
if(bfs(s, t)) return flow;
memcpy(iter, head, sizeof head);
flow += dfs(s, t, INF);
}
}
int main()
{
int f,d;
while(~scanf("%d%d%d",&n,&f,&d))
{
cnt=0;
memset(head, -1, sizeof head);
int s=0,t=n+f+n+d+1;
for(int i=1;i<=n;i++)
{
add_edge(i+f,i+f+n,1);//牛1和牛11；
}
for(int i=1; i<=f; i++)
{
add_edge(s,i,1);//起点和饭;
}
for(int i=1; i<=d; i++)
{
add_edge(i+f+n+n,t,1);//菜和终点；
}
for(int i=1; i<=n; i++)
{
int f1,d1;
scanf("%d%d",&f1,&d1);
for(int j=1; j<=f1; j++)//饭和牛1
{
scanf("%d",&a[j]);
add_edge(a[j],i+f,1);
}
for(int j=1; j<=d1; j++)//牛11和菜
{
scanf("%d",&b[j]);
add_edge(i+f+n,b[j]+f+n+n,1);
}
}
printf("%d\n",dinic(s,t));
}
}