二分图裸题,找他的最大匹配即可

#include
     
      using namespace std;int n,m,ans;const int N=1e6+7;int to[N];struct node{    int to,nex;}e[N];int x,y,tot;int head[N];bool vis[N];void add(int a,int b){    e[++tot].to=b;    e[tot].nex=head[a];    head[a]=tot;}bool dfs(int x){    for(int i=head[x];i;i=e[i].nex)    {        int xx=e[i].to;        if(!vis[xx])        {            vis[xx]=1;            if(!to[xx]||dfs(to[xx]))            {                to[xx]=x;                return 1;            }        }    }    return 0;}int main(){    cin>>n>>m;    cin>>x>>y;    while(x!=-1&&y!=-1)    {        if(x<=n&&y<=m) add(x,y);        cin>>x;cin>>y;    }    for(int i=1;i<=n;i++)    {        memset(vis,0,sizeof(vis));        if(dfs(i)) ans++;    }    cout<
      
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