P2756 飞行员配对方案问题(二分图)

Posted 2022-05-24 Harris-H

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;