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：

 1 # include <cstdio>
 2 # include <cstring>
 3 # include <algorithm>
 4 # include <iostream>
 5 using namespace std;
 6 
 7 int list[1020],dis[1020],gap[1020],node;
 8 int source,sink,Vs,inf = 1 << 30;
 9 int N,M,T,C;
10 struct E
11 {
12     int to,c,next;
13 }edg[100002];
14 
15 void addedg(int from,int to,int value)
16 {
17     edg[node].to = to,edg[node].c = value,edg[node].next = list[from],list[from] = node++;
18     edg[node].to = from,edg[node].c = 0,edg[node].next = list[to],list[to] = node ++;
19 }
20 
21 int dfs(int src,int aug)
22 {
23     if(src == sink) return aug;
24 
25     int flow = 0,mid_d = Vs-1;
26     for(int j = list[src];j != -1; j = edg[j].next)
27         if(edg[j].c)
28         {
29             if(dis[src] == dis[edg[j].to]+1)
30             {
31                 int t = dfs(edg[j].to,min(aug-flow,edg[j].c));
32 
33                 edg[j].c -= t;
34                 edg[j^1].c += t;
35                 flow += t;
36                 if(dis[source] >= Vs)    return flow;
37                 if(aug == flow) break;
38             }
39             mid_d = min(mid_d,dis[edg[j].to]);
40         }
41     if(!flow)
42     {
43         if(!(--gap[dis[src]]))    dis[source] = Vs;
44         dis[src] = mid_d+1;
45         ++gap[dis[src]];
46     }
47     return flow;
48 }
49 
50 bool maxflow_sap(int src,int ed)
51 {
52     int ans = 0;
53     memset(gap,0,sizeof(gap));
54     memset(dis,0,sizeof(dis));
55     gap[0] = Vs = ed;
56     source = src, sink = ed;
57 
58     while(dis[source] < Vs)
59     {
60         //printf("%d %d\n",T,ans);
61         if(dfs(source,inf))
62         T--;
63         if(T<=0) break;
64     }
65     if(T<=0) return true;
66     return false;
67 
68 }
69 
70 int main()
71 {
72     //freopen("a.txt","r",stdin);
73     while(~scanf("%d%d%d%d",&N,&M,&T,&C))
74     {
75         int i,j;
76         node = 0;
77         memset(list,-1,sizeof(list));
78         for(i = 0;i < M;i++)
79         {
80             int x,y,c;
81             scanf("%d%d%d",&x,&y,&c);
82            // printf("%d%d%d\n",x,y,c);
83             if(c<=C) addedg(x,y,c);
84         }
85         if(maxflow_sap(1,N)) printf("YES\n");
86         else printf("NO\n");
87     }
88     return 0;
89 }

 

posted @ 2015-06-10 17:13  NowAndForever  阅读(189)  评论(0)  编辑  收藏  举报