sgu 176 Flow construction（有源汇的上下界最小流）

  1 #include<set>
  2 #include<cmath>
  3 #include<queue>
  4 #include<vector>
  5 #include<cstdio>
  6 #include<cstring>
  7 #include<iostream>
  8 #include<algorithm>
  9 #define trav(u,i) for(int i=front[u];i;i=e[i].nxt)
 10 #define FOR(a,b,c) for(int a=(b);a<=(c);a++)
 11 using namespace std;
 12 
 13 typedef long long ll;
 14 const int N = 5e4+10;
 15 const int inf = 1e9;
 16 
 17 ll read() {
 18     char c=getchar();
 19     ll f=1,x=0;
 20     while(!isdigit(c)) {
 21         if(c==‘-‘) f=-1; c=getchar();
 22     }
 23     while(isdigit(c))
 24         x=x*10+c-‘0‘,c=getchar();
 25     return x*f;
 26 }
 27 
 28 struct Edge {
 29     int u,v,cap,flow;
 30     Edge(int u=0,int v=0,int cap=0,int flow=0)
 31         :u(u),v(v),cap(cap),flow(flow){}
 32 };
 33 struct Dinic {
 34     int n,m,s,t;
 35     int d[N],cur[N],vis[N];
 36     vector<int> g[N];
 37     vector<Edge> es;
 38     queue<int> q;
 39     void init(int n) {
 40         this->n=n;
 41         es.clear();
 42         FOR(i,0,n) g[i].clear();
 43     }
 44     void clear() {
 45         FOR(i,0,(int)es.size()-1) es[i].flow=0;
 46     }
 47     void AddEdge(int u,int v,int w) {
 48         es.push_back(Edge(u,v,w,0));
 49         es.push_back(Edge(v,u,0,0));
 50         m=es.size();
 51         g[u].push_back(m-2);
 52         g[v].push_back(m-1);
 53     }
 54     int bfs() {
 55         memset(vis,0,sizeof(vis));
 56         q.push(s); d[s]=0; vis[s]=1;
 57         while(!q.empty()) {
 58             int u=q.front(); q.pop();
 59             FOR(i,0,(int)g[u].size()-1) {
 60                 Edge& e=es[g[u][i]];
 61                 int v=e.v;
 62                 if(!vis[v]&&e.cap>e.flow) {
 63                     vis[v]=1;
 64                     d[v]=d[u]+1;
 65                     q.push(v);
 66                 }
 67             }
 68         }
 69         return vis[t];
 70     }
 71     int dfs(int u,int a) {
 72         if(u==t||!a) return a;
 73         int flow=0,f;
 74         for(int& i=cur[u];i<g[u].size();i++) {
 75             Edge& e=es[g[u][i]];
 76             int v=e.v;
 77             if(d[v]==d[u]+1&&(f=dfs(v,min(a,e.cap-e.flow)))>0) {
 78                 e.flow+=f; 
 79                 es[g[u][i]^1].flow-=f;
 80                 flow+=f; a-=f;
 81                 if(!a) break;
 82             }
 83         }
 84         return flow;
 85     }
 86     int MaxFlow(int s,int t) {
 87         this->s=s,this->t=t;
 88         int flow=0;
 89         while(bfs()) {
 90             memset(cur,0,sizeof(cur));
 91             flow+=dfs(s,inf);
 92         }
 93         return flow;
 94     }
 95 } dc;
 96 
 97 int n,m,sum,down[N],in[N],id[N];
 98 
 99 int main()
100 {
101     while(scanf("%d%d",&n,&m)==2) {
102         sum=0;
103         int S=0,T=n+1;
104         dc.init(T+2);
105         memset(in,0,sizeof(in));
106         FOR(i,1,m) {
107             id[i]=-1;
108             int x=read(),y=read(),z=read(),c=read();
109             if(c) down[i]=z,sum+=z,dc.AddEdge(S,y,z),dc.AddEdge(x,T,z);
110             else down[i]=0,dc.AddEdge(x,y,z),id[i]=dc.es.size()-2;
111         }
112         int flow=dc.MaxFlow(S,T);
113         dc.AddEdge(n,1,inf);
114         flow+=dc.MaxFlow(S,T);
115         if(flow!=sum) puts("Impossible");
116         else {
117             printf("%d\n",dc.es[dc.es.size()-2].flow);
118             FOR(i,1,m-1) 
119                 if(id[i]>=0) printf("%d ",dc.es[id[i]].flow+down[i]);
120                 else printf("%d ",down[i]);
121             if(id[m]>=0) printf("%d\n",dc.es[id[m]].flow+down[m]);
122             else printf("%d\n",down[m]);
123         }
124     }
125     return 0;
126 }