二分图最大匹配 网络流&匈牙利

  1 #include<cstdio> 
  2 #include<cstring>
  3 #include<cmath>
  4 #include<ctime>
  5 #include<iostream>
  6 #include<algorithm>
  7 #include<queue>
  8 #include<set>
  9 #define inf (0x7fffffff)
 10 #define maxint (2147483647)
 11 #define l(a) ((a)<<1)
 12 #define r(a) ((a)<<1|1)
 13 #define b(a) (1<<(a))
 14 #define rep(i,a,b) for(int i=a;i<=(b);i++)
 15 #define clr(a) memset(a,0,sizeof(a))
 16 typedef long long ll;
 17 using namespace std;
 18 int readint(){
 19     int t=0,f=1;char c=getchar();
 20     while(!isdigit(c)){
 21         if(c==‘-‘) f=-1;
 22         c=getchar();
 23     }
 24     while(isdigit(c)){
 25         t=(t<<3)+(t<<1)+c-‘0‘;
 26         c=getchar();
 27     }
 28     return t*f;
 29 }
 30 ll readll(){
 31     ll t=0ll,f=1ll;char c=getchar();
 32     while(!isdigit(c)){
 33         if(c==‘-‘) f=-1ll;
 34         c=getchar();
 35     }
 36     while(isdigit(c)){
 37         t=(t<<3ll)+(t<<1ll)+ll(c-‘0‘);
 38         c=getchar();
 39     }
 40     return t*f;
 41 }
 42 const int maxn=5009,maxe=1000009;
 43 int n,m,en,S,T,ans,d[maxn];
 44 struct edge{
 45     int v,w;
 46     edge*next,*r;
 47     inline edge(int V,int W){
 48         v=V;w=W;
 49     }
 50     inline edge(){};
 51 }E[maxe],*pt=E,*fir[maxn],*cur[maxn];
 52 void add(int u,int v,int w){
 53     pt->v=v;pt->w=w;
 54     pt->next=fir[u];fir[u]=pt++;
 55 }
 56 void addedge(int u,int v,int w){
 57     add(u,v,w);add(v,u,0);
 58     fir[u]->r=fir[v];fir[v]->r=fir[u];
 59 }
 60 bool Bfs(){
 61     rep(i,S,T) d[i]=0;
 62     queue<int>Q;Q.push(S);d[S]=1;
 63     while(!Q.empty()){
 64         int x=Q.front();Q.pop();
 65         for(edge*e=fir[x];e;e=e->next) if(e->w&&!d[e->v]){
 66             d[e->v]=d[x]+1;Q.push(e->v);
 67         }
 68     }
 69     return d[T];
 70 }
 71 int Dfs(int x,int f){
 72     if(x==T||!f) return f;
 73     int t=0;
 74     for(edge*&e=cur[x];e;e=e->next) if(e->w&&d[e->v]==d[x]+1){
 75         int g=Dfs(e->v,min(f,e->w));
 76         if(g){
 77             e->w-=g;e->r->w+=g;
 78             t+=g;f-=g;
 79             if(!f) break;
 80         }
 81     }
 82     return t;
 83 }
 84 void Dinic(){
 85     while(Bfs()){
 86         rep(i,S,T) cur[i]=fir[i];
 87         ans+=Dfs(S,inf);
 88     }
 89 }
 90 int main(){
 91     //freopen("#input.txt","r",stdin);
 92     //freopen("#output.txt","w",stdout);
 93     n=readint();m=readint();en=readint();S=0;T=n+m+1;
 94     rep(i,1,en){
 95         int U=readint(),V=readint();
 96         if(V>m) continue;
 97         addedge(U,n+V,1);
 98     }
 99     rep(i,1,n) addedge(S,i,1);
100     rep(i,1,m) addedge(n+i,T,1);
101     Dinic();
102     cout<<ans<<endl;
103     //fclose(stdin);
104     //fclose(stdout);
105     return 0;
106 }