P2756 飞行员配对方案问题 网络流

P2756 飞行员配对方案问题

 #include <bits/stdc++.h>
 using namespace std;
 const int maxn = , inf = 0x3f3f3f;
 struct Edge {
     int from, to, cap, flow;
 };

 struct Dinic {
     int n, m, s, t;
     vector<Edge> edges;
     vector<int> G[maxn];
     bool vis[maxn];
     int d[maxn];
     int cur[maxn];

     void AddEdge(int from, int to, int cap) {
         edges.push_back((Edge){from, to, cap, });
         edges.push_back((Edge){to, from, , });
         m = edges.size();
         G[from].push_back(m-);
         G[to].push_back(m-);
     }
     bool bfs() {
         memset(vis, , sizeof(vis));
         queue<int> que;
         que.push(s);
         d[s] = ;
         vis[s] = true;
         while (!que.empty()) {
             int x = que.front(); que.pop();
             for (int i = ; i < G[x].size(); ++i) {
                 Edge& e = edges[G[x][i]];
                 if (!vis[e.to] && e.cap > e.flow) {
                     vis[e.to] = true;
                     d[e.to] = d[x] + ;
                     que.push(e.to);
                 }
             }
         }
         return vis[t];
     }
     int dfs(int x, int a) {
         if (x == t || a == ) return a;
         int flow = , f;
         for (int& i = cur[x]; i < G[x].size(); ++i) {
             Edge& e = edges[G[x][i]];
             if (d[x] +  == d[e.to] && (f = dfs(e.to, min(a, e.cap-e.flow))) > ) {
                 e.flow += f;
                 edges[G[x][i]^].flow -= f;
                 flow += f;
                 a -= f;
                 if (a == ) break;
             }
         }
         return flow;
     }
     int maxflow(int s, int t) {
         this->s = s; this->t = t;
         int flow = ;
         while (bfs()) {
             memset(cur,,sizeof(cur));
             flow += dfs(s,inf);
         }
         return flow;
     }
 }dinic;
 int main() {
     int m, n; scanf("%d%d",&m,&n);
     while (true) {
         int i, j; scanf("%d%d",&i,&j);
         if (i == - && j == -) break;
         dinic.AddEdge(i,j,);
     }
     int s = n+, t = n+;
     for (int i = ; i <= m; ++i) {
         dinic.AddEdge(s,i,);
     }
     for (int i = m+; i <= n; ++i) {
         dinic.AddEdge(i,t,);
     }
     int ans = dinic.maxflow(s,t);
     if (ans == ) puts("No Solution!");
     else {
         printf("%d\n",ans);
         for (int i = ; i < dinic.edges.size(); ++i) {
             if (dinic.edges[i].from == s) continue;
             if (dinic.edges[i].to == t) continue;
             if (dinic.edges[i].flow == ) {
                 printf("%d %d\n",dinic.edges[i].from,dinic.edges[i].to);
             }
         }
     }
     return ;
 }