hunnu - 11545 小明的烦恼——找路径 (最大流)

http://acm.hunnu.edu.cn/online/?action=problem&type=show&id=11545

只是要求不经过相同的边,那么每次找出一条增广路T--,判断T<=0即可.

在加边的时候注意要c<=C的时候才需要加边.

邻接表：

 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <iostream>
 using namespace std;

 int list[],dis[],gap[],node;
 int source,sink,Vs,inf =  << ;
 int N,M,T,C;
 struct E
 {
     int to,c,next;
 }edg[];

 void addedg(int from,int to,int value)
 {
     edg[node].to = to,edg[node].c = value,edg[node].next = list[from],list[from] = node++;
     edg[node].to = from,edg[node].c = ,edg[node].next = list[to],list[to] = node ++;
 }

 int dfs(int src,int aug)
 {
     if(src == sink) return aug;

     int flow = ,mid_d = Vs-;
     for(int j = list[src];j != -; j = edg[j].next)
         if(edg[j].c)
         {
             if(dis[src] == dis[edg[j].to]+)
             {
                 int t = dfs(edg[j].to,min(aug-flow,edg[j].c));

                 edg[j].c -= t;
                 edg[j^].c += t;
                 flow += t;
                 if(dis[source] >= Vs)    return flow;
                 if(aug == flow) break;
             }
             mid_d = min(mid_d,dis[edg[j].to]);
         }
     if(!flow)
     {
         if(!(--gap[dis[src]]))    dis[source] = Vs;
         dis[src] = mid_d+;
         ++gap[dis[src]];
     }
     return flow;
 }

 bool maxflow_sap(int src,int ed)
 {
     int ans = ;
     memset(gap,,sizeof(gap));
     memset(dis,,sizeof(dis));
     gap[] = Vs = ed;
     source = src, sink = ed;

     while(dis[source] < Vs)
     {
         //printf("%d %d\n",T,ans);
         if(dfs(source,inf))
         T--;
         if(T<=) break;
     }
     if(T<=) return true;
     return false;

 }

 int main()
 {
     //freopen("a.txt","r",stdin);
     while(~scanf("%d%d%d%d",&N,&M,&T,&C))
     {
         int i,j;
         node = ;
         memset(list,-,sizeof(list));
         for(i = ;i < M;i++)
         {
             int x,y,c;
             scanf("%d%d%d",&x,&y,&c);
            // printf("%d%d%d\n",x,y,c);
             if(c<=C) addedg(x,y,c);
         }
         if(maxflow_sap(,N)) printf("YES\n");
         else printf("NO\n");
     }
     return ;
 }