cogs_14_搭配飞行员_(二分图匹配+最大流,网络流24题#01)

#include <bits/stdc++.h>
using namespace std; const int maxn=+,INF=0x7fffffff;
int n,m,cnt=;
int lvl[maxn],itr[maxn],head[maxn];
struct edge{
int to,cap,next;
edge(){}
edge(int to,int cap,int next):to(to),cap(cap),next(next){}
}g[maxn*maxn*];
void add_edge(int u,int v,int cap){
g[++cnt]=edge(v,cap,head[u]); head[u]=cnt;
g[++cnt]=edge(u,,head[v]); head[v]=cnt;
}
void bfs(int s){
memset(lvl,-,sizeof lvl);
lvl[s]=;
queue <int> q;
q.push(s);
while(!q.empty()){
int u=q.front(); q.pop();
for(int i=head[u];i;i=g[i].next){
int v=g[i].to;
if(lvl[v]<&&g[i].cap>){
lvl[v]=lvl[u]+;
q.push(v);
}
}
}
}
int dfs(int u,int t,int f){
if(u==t) return f;
for(int &i=itr[u];i;i=g[i].next){
int v=g[i].to;
if(g[i].cap>&&lvl[u]<lvl[v]){
int d=dfs(v,t,min(f,g[i].cap));
if(d>){
g[i].cap-=d;
g[i^].cap+=d;
return d;
}
}
}
return ;
}
int max_flow(int s,int t){
int flow=;
for(bfs(s);lvl[t]>;bfs(s)){
for(int i=;i<=n+;i++) itr[i]=head[i];
int f;
while((f=dfs(s,t,INF))>) flow+=f;
}
return flow;
}
void init(){
scanf("%d%d",&n,&m);
for(int i=;i<=m;i++) add_edge(,i,);
for(int i=m+;i<=n;i++) add_edge(i,n+,);
int u,v;
while(scanf("%d%d",&u,&v)!=EOF) add_edge(u,v,);
}
int main(){
freopen("flyer.in","r",stdin);
freopen("flyer.out","w",stdout);
init();
printf("%d\n",max_flow(,n+));
fclose(stdin);
fclose(stdout);
return ;
}