ACdream 1017 Fast Transportation

http://acdream.info/problem?pid=1017

题意:给n个点，m条边，K个货物，要从从S到T，每天每条边最多只能经过1次，求要几天能运完

思路:拆成分层图，每层向下一层连边，注意i也能连到i，流量为inf，代表这个点的货车这天没动

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #define inf 0x7fffffff
 struct edge{
     int u,v;
 }e[];
 int tot,go[],next[],first[],op[],flow[],dis[],cnt[];
 int T,S,ss,tt,n,m,nodes,K;
 int id[][];
 int read(){
     int t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 void insert(int x,int y,int z){
     tot++;
     go[tot]=y;
     next[tot]=first[x];
     first[x]=tot;
     flow[tot]=z;
 }
 void add(int x,int y,int z){
     insert(x,y,z);op[tot]=tot+;
     insert(y,x,);op[tot]=tot-;
 }
 int dfs(int x,int f){
     if (x==T) return f;
     int mn=nodes,sum=;
     for (int i=first[x];i;i=next[i]){
          int pur=go[i];
          if (flow[i]&&dis[pur]+==dis[x]){
              int save=dfs(pur,std::min(flow[i],f-sum));
              flow[i]-=save;
              flow[op[i]]+=save;
              sum+=save;
              if (dis[S]>=nodes||f==sum) return sum;
          }
          if (flow[i]) mn=std::min(mn,dis[pur]);
     }
     if (sum==){
         cnt[dis[x]]--;
         if (cnt[dis[x]]==){
            dis[S]=nodes;
         }else{
            dis[x]=mn+;
            cnt[dis[x]]++;
         }
     }
     return sum;
 }
 bool check(int mid){
     for (int i=;i<=nodes;i++) first[i]=cnt[i]=dis[i]=;tot=;
     int sz=;
     for (int i=;i<=mid;i++)
         for (int j=;j<=n;j++)
             id[i][j]=++sz;
     T=sz+;
     sz+=;
     S=;nodes=sz;
     add(S,id[][ss],K);
     for (int i=;i<=mid;i++)
         add(id[i][tt],T,K);
     for (int i=;i<mid;i++)
      for (int j=;j<=n;j++)
       add(id[i][j],id[i+][j],inf);
     for (int i=;i<=m;i++)
         for (int j=;j<mid;j++)
             add(id[j][e[i].u],id[j+][e[i].v],),add(id[j][e[i].v],id[j+][e[i].u],);
     int Ans=;
     while (dis[S]<nodes) Ans+=dfs(S,inf);
     return Ans==K;
 }
 int main(){
     while (scanf("%d",&n)!=EOF){
          m=read();K=read();ss=read();tt=read();
          for (int i=;i<=m;i++)
             e[i].u=read(),e[i].v=read();
          int l=,r=n+K+,ans=;
          while (l<=r){
             int mid=(l+r)/;
             if (check(mid)) r=mid-,ans=mid;
                 else l=mid+;
           }
           printf("%d\n",ans-);
     }
 }