P2756 飞行员配对方案问题(二分图)

P2756 飞行员配对方案问题(二分图)

经典二分图匹配板题。

// Problem: P2756 飞行员配对方案问题
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P2756
// Memory Limit: 125 MB
// Time Limit: 1000 ms
// Date: 2022-05-20 11:36:24
// --------by Herio--------

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull; 
const int N=1e3+5,M=2e4+5,inf=0x3f3f3f3f,mod=1e9+7;
const int hashmod[4] = {402653189,805306457,1610612741,998244353};
#define mst(a,b) memset(a,b,sizeof a)
#define db double
#define PII pair<int,int>
#define PLL pair<ll,ll>
#define x first
#define y second
#define pb emplace_back
#define SZ(a) (int)a.size()
#define rep(i,a,b) for(int i=a;i<=b;++i)
#define per(i,a,b) for(int i=a;i>=b;--i)
#define IOS ios::sync_with_stdio(false),cin.tie(nullptr) 
void Print(int *a,int n){
  for(int i=1;i<n;i++)
    printf("%d ",a[i]);
  printf("%d\n",a[n]); 
}
template <typename T>   //x=max(x,y)  x=min(x,y)
void cmx(T &x,T y){
  if(x<y) x=y;
}
template <typename T>
void cmn(T &x,T y){
  if(x>y) x=y;
}
struct node{
  int to,nt;
}e[M];
int cnt,h[N];
void add(int u,int v){
  e[++cnt]={v,h[u]},h[u]=cnt;
}
int vis[N],mh[N];
int ans[N];
bool find(int u){
  for(int i=h[u];i;i=e[i].nt){
    if(vis[e[i].to]) continue;
    int v=e[i].to;
    vis[v]=1;
    if(!mh[v]||find(mh[v])){
      mh[v]=u;
      ans[u]=v;
      return true;
    }
  }
  return false;
}

int main(){
  int m,n;
  scanf("%d%d",&m,&n);
  int u,v;
  while(~scanf("%d%d",&u,&v)){
    if(u==-1&&v==-1) break;
    add(u,v);
  }
  int k = 0;
  rep(i,1,m){ 
    mst(vis,0);
    if(find(i)) k++;
  }
  printf("%d\n",k);
  rep(i,1,m){
    if(ans[i]) printf("%d %d\n",i,ans[i]);
  }
  return 0;
}