[网络流24题] 飞行员配对方案问题 二分图/最大流

题目链接

建立二分图,跑一边最大流即可,最后再根据流量路径输出

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

const int  MAXN = 41000;
const int  MAXM = 10000010;
const int  INF  = 0x3f3f3f3f;

//const ll MOD = 998244353;





inline int read(){int ra,fh;char rx;rx=getchar(),ra=0,fh=1;
while((rx<'0'||rx>'9')&&rx!='-')rx=getchar();if(rx=='-')
fh=-1,rx=getchar();while(rx>='0'&&rx<='9')ra*=10,ra+=rx-48,
rx=getchar();return ra*fh;}


struct Edge
{
    int from, to, cap, flow, next;
};
Edge edge[MAXM];
int head[MAXN], cur[MAXN], edgenum;
int dist[MAXN];
bool vis[MAXN];
int N, M,ss,tt;
void init()
{
    edgenum = 0;
    memset(head, -1, sizeof(head));
}
void addEdge(int u, int v, int w)
{
    Edge E1 = {u, v, w, 0, head[u]};
    edge[edgenum] = E1;
    head[u] = edgenum++;
    Edge E2 = {v, u, 0, 0, head[v]};
    edge[edgenum] = E2;
    head[v] = edgenum++;
}

bool BFS(int s, int t)
{
    queue<int> Q;
    memset(dist, -1, sizeof(dist));
    memset(vis, false, sizeof(vis));
    dist[s] = 0;
    vis[s] = true;
    Q.push(s);
    while(!Q.empty())
    {
        int u = Q.front();
        Q.pop();
        for(int i = head[u]; i != -1; i = edge[i].next)
        {
            Edge E = edge[i];
            if(!vis[E.to] && E.cap > E.flow)
            {
                dist[E.to] = dist[u] + 1;
                if(E.to == t) return true;
                vis[E.to] = true;
                Q.push(E.to);
            }
        }
    }
    return false;
}
int DFS(int x, int a, int t)
{
    if(x == t || a == 0) return a;
    int flow = 0, f;
    for(int &i = cur[x]; i != -1; i = edge[i].next)
    {
        Edge &E = edge[i];
        if(dist[E.to] == dist[x] + 1 && (f = DFS(E.to, min(a, E.cap - E.flow), t)) > 0)
        {
            edge[i].flow += f;
            edge[i^1].flow -= f;
            flow += f;
            a -= f;
            if(a == 0) break;
        }
    }
    return flow;
}
int Maxflow(int s, int t)
{
    int flow = 0;
    while(BFS(s, t))
    {
        memcpy(cur, head, sizeof(head));
        flow += DFS(s, INF, t);
    }
    return flow;
}



int m,n;


int main()
{
//    freopen("data.txt","r",stdin);
    ios_base::sync_with_stdio(false);
    cin >> m>>n;
    init();
    int s = 0;
    int t = n+1;
    for(int i=1;i<=m;i++)
    {
        addEdge(s,i,1);
    }

    for(int i=m+1;i<=n;i++)
    {
        addEdge(i,t,1);
    }
    int u,v;
    while(cin >> u >>v)
    {
        if(u==-1 && v==-1)
            break;
        addEdge(u,v,1);
    }
    int ans =Maxflow(s,t);
    if(ans==0)
    {
        cout <<"No Solution!"<<endl;
        continue;
    }
    cout<< ans<<endl;

    for(int k=1;k<=m;k++)
    {
        for(int i = head[k]; i != -1; i = edge[i].next)
        {
            if(edge[i].flow==1)
            {
                cout << k <<" "<<edge[i].to<<endl;
//                break;
            }
        }
    }

    return 0;
}