洛谷P3386 【模板】二分图匹配

//minamoto
#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#define inf 0x3f3f3f3f
using namespace std;
#define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
char buf[1<<21],*p1=buf,*p2=buf;
inline int read(){
#define num ch-'0'
char ch;bool flag=0;int res;
while(!isdigit(ch=getc()))
(ch=='-')&&(flag=true);
for(res=num;isdigit(ch=getc());res=res*10+num);
(flag)&&(res=-res);
#undef num
return res;
}
const int N=2005,M=2100005;
int ver[M],Next[M],head
,edge[M],tot=1;
int dep
,cur
,s,t;
int n,m,k;
queue<int> q;
inline void add(int u,int v,int e){
ver[++tot]=v,Next[tot]=head[u],head[u]=tot,edge[tot]=e;
ver[++tot]=u,Next[tot]=head[v],head[v]=tot,edge[tot]=0;
}
bool bfs(){
memset(dep,-1,sizeof(dep));
while(!q.empty()) q.pop();
for(int i=s;i<=t;++i) cur[i]=head[i];
q.push(s),dep[s]=0;
while(!q.empty()){
int u=q.front();q.pop();
for(int i=head[u];i;i=Next[i]){
int v=ver[i];
if(dep[v]<0&&edge[i]){
dep[v]=dep[u]+1,q.push(v);
if(v==t) return true;
}
}
}
return false;
}
int dfs(int u,int limit){
if(!limit||u==t) return limit;
int flow=0,f;
for(int i=cur[u];i;i=Next[i]){
int v=ver[i];cur[u]=i;
if(dep[v]==dep[u]+1&&(f=dfs(v,min(limit,edge[i])))){
flow+=f,limit-=f;
edge[i]-=f,edge[i^1]+=f;
if(!limit) break;
}
}
return flow;
}
int dinic(){
int flow=0;
while(bfs()) flow+=dfs(s,inf);
return flow;
}
int main(){
n=read(),m=read(),k=read();
s=0,t=n+m+1;
for(int i=1;i<=n;++i) add(s,i,1);
for(int i=n+1;i<=n+m;++i) add(i,t,1);
for(int i=1;i<=k;++i){
int u=read(),v=read();
if(v>m) continue;
add(u,v+n,1);
}
printf("%d\n",dinic());
return 0;
}