P3386 【模板】二分图最大匹配

2021年09月15日 阅读数：3

```#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define ls rt<<1
#define rs rt<<1|1
#define lson ls,nl,mid,l,r
#define rson rs,mid+1,nr,l,r
#define N 1000010
#define For(i,a,b) for(long long i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()

using namespace std;
long long n,m,x,y,v,k;

void in(long long &x){
long long y=1;char c=getchar();x=0;
while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();}
while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();}
x*=y;
}
void o(long long x){
if(x<0){p('-');x=-x;}
if(x>9)o(x/10);
p(x%10+'0');
}

struct Dinic{
long long maxflow,tot;
queue<long long>q;

struct node{
long long n;
long long v;
long long next;
}e[N];

void init(){
}

void push(long long x,long long y,long long v){
e[tot].n=y;
e[tot].v=v;
}
bool bfs(long long s,long long t){
memset(deep,-1,sizeof(deep));
For(i,0,n+m+2)
deep[s]=0;
q.push(s);
while(!q.empty()){
long long now=q.front();
q.pop();
if(deep[e[i].n]==-1 && e[i].v>0){
deep[e[i].n]=deep[now]+1;
q.push(e[i].n);
}
}
return deep[t]!=-1;
}

long long dfs(long long now,long long t,long long lim){
if(now==t||lim==0)
return lim;
long long flow=0,f;
for(long long i=cur[now];i!=-1;i=e[i].next){
cur[now]=i;
if(deep[e[i].n]==deep[now]+1 && (f=dfs(e[i].n,t, min(lim,e[i].v) ))){
flow+=f;
lim-=f;
e[i].v-=f;
e[i^1].v+=f;
if(!lim) break;
}
}
return flow;
}

void dinic(long long s,long long t){
while(bfs(s,t)){
maxflow+=dfs(s,t,inf);
}
}
}g;

int main(){
in(n);in(m);in(k);
g.init();
For(i,1,n){
g.push(0,i,1);
g.push(i,0,0);
}
For(i,1,m){
g.push(i+n,n+m+1,1);
g.push(n+m+1,n+i,0);
}
For(i,1,k){
in(x);in(y);
g.push(x,y+n,1);
g.push(y+n,x,0);
}
g.dinic(0,n+m+1);
o(g.maxflow);
return 0;
}```