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;

}