洛谷P2756 飞行员配对方案问题 网络流_二分图
Code:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 | #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; } |
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