洛谷P2756 飞行员配对方案问题 网络流_二分图

Code:

#include<cstdio>
#include<queue>
#include<vector>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=203;
const int INF=100000+233;
int s,t;
int mapp[maxn];
struct Edge{
	int from,to,cap;
	Edge(int u,int v,int c):from(u),to(v),cap(c){}
};
vector<Edge>edges;
struct Dicnic{
    vector<int>G[maxn];
    queue<int>Q;
    int d[maxn],vis[maxn],p[maxn],cur[maxn];
    void addedge(int u,int v,int c){
    	edges.push_back(Edge(u,v,c));
    	edges.push_back(Edge(v,u,0));
    	int m=edges.size();
    	G[u].push_back(m-2);
    	G[v].push_back(m-1);
    }
    int BFS(){
        memset(vis,0,sizeof(vis));
        Q.push(s);vis[s]=1,d[s]=0;
        while(!Q.empty()){
        	int u=Q.front();Q.pop();
        	int sz=G[u].size();
        	for(int i=0;i<sz;++i)
        	{
                Edge e=edges[G[u][i]];
                if(e.cap>0&&!vis[e.to]){
                	d[e.to]=d[u]+1,vis[e.to]=1;
                	Q.push(e.to);
                }
        	}
        }
        return vis[t];
    }
    int dfs(int x,int a)
    {
    	if(x==t)return a;
        int sz=G[x].size();
        int flow=0;
        for(int i=cur[x];i<sz;++i){
        	Edge e=edges[G[x][i]];
        	if(d[e.to]==d[x]+1&&e.cap>0){
        		int f=dfs(e.to,min(a,e.cap));
        		if(f>0){
        			int u=G[x][i];
        			a-=f,flow+=f;
                    edges[u].cap-=f;
                    edges[u^1].cap+=f;
                    if(a==0)break;
        		}
        	}
        }
        return flow;
    }
    int maxflow(){
    	memset(cur,0,sizeof(cur));
    	int ans=0;
    	while(BFS())ans+=dfs(s,INF);
    	return ans;
    }
};
int main()
{

     int n,m;
     Dicnic op;
     scanf("%d%d",&m,&n);
     s=0,t=m+n+1;
     for(int i=1;i<=m;++i)op.addedge(s,i,1);
     for(int i=m+1;i<=n+m;++i)op.addedge(i,t,1);
     while(233)
     {
     	int a,b;scanf("%d%d",&a,&b);
     	if(a<0||b<0)break;
     	op.addedge(a,b,1);
     }
     int ans=op.maxflow();
     if(ans==0){
     	printf("No Solution!\n");
     	return 0;
     }
     printf("%d\n",ans);
     int sz=edges.size();
     for(int i=n+n+m+m;i<sz;i+=2){
        if(edges[i].cap==0)mapp[edges[i].from]=edges[i].to;
     }
     for(int i=1;i<=m;++i)
        if(mapp[i])printf("%d %d\n",i,mapp[i]);
     return 0;
}