HDU 3549 Flow Problem 网络流 ISAP

http://acm.hdu.edu.cn/showproblem.php?pid=3549

题意：

　　给出N个点M条边，求1到N的最大流量。

 

坑爹:

　　模板

 

解法：

　　在白书上看到的ISAP算法就敲了个模板出来A了这道题，就是想测试一下EK和ISAP的时间

差多少，EK是921MS，ISAP是109MS。

 

  1 #include<iostream>
  2 #include<stdio.h>
  3 #include<vector>
  4 #include<queue>
  5 using namespace std;
  6 
  7 const int maxn = 1000 + 10;
  8 const int INF = 0x3fffffff;
  9 
 10 struct Edge {
 11     int from;
 12     int to;
 13     int cap;
 14     int flow;
 15 }edge[2*maxn];
 16 vector<int> G[maxn];
 17 int head[maxn];
 18 int cur[maxn];
 19 bool used[maxn];
 20 int deep[maxn];
 21 int front[maxn];
 22 int gap[maxn];
 23 int cnt;
 24 int N;
 25 int M;
 26 
 27 void addEdge(int from, int to, int cap)
 28 {
 29     edge[cnt].from = from;
 30     edge[cnt].to = to;
 31     edge[cnt].cap = cap;
 32     edge[cnt].flow = 0;
 33     cnt ++;
 34 
 35     edge[cnt].from = to;
 36     edge[cnt].to = from;
 37     edge[cnt].cap = 0;
 38     edge[cnt].flow = 0;
 39     cnt ++;
 40 
 41     G[from].push_back(cnt-2);
 42     G[to].push_back(cnt-1);
 43 }
 44 
 45 bool BFS(int s, int t)
 46 {
 47     memset(used,0,sizeof(used));
 48     queue<int> Q;
 49     Q.push(t);
 50     deep[t] = 0;
 51     used[t] = true;
 52     while(!Q.empty())
 53     {
 54         int top = Q.front();
 55         Q.pop();
 56         int i;
 57         for(i=0; i<G[top].size(); i++)
 58         {
 59             Edge e = edge[G[top][i]];
 60             if(!used[e.to])
 61             {
 62                 used[e.to] = true;
 63                 deep[e.to] = deep[top] + 1;
 64                 Q.push(e.to);
 65             }
 66         }
 67     }
 68     return used[s];
 69 }
 70 
 71 int Augment(int s,int t)
 72 {
 73     int begin = t;
 74     int minFlow = INF;
 75     while(begin != s)
 76     {
 77         Edge& e = edge[front[begin]];
 78         minFlow = min(minFlow, e.cap-e.flow);
 79         begin = edge[front[begin]].from;
 80     }
 81     begin = t;
 82     while(begin != s)
 83     {
 84         edge[front[begin]].flow += minFlow;
 85         edge[front[begin]^1].flow -= minFlow;
 86         begin = edge[front[begin]].from;
 87     }
 88     return minFlow;
 89 }
 90 
 91 int Maxflow(int s,int t)
 92 {
 93     int flow = 0;
 94     BFS(s,t);
 95     memset(gap,0,sizeof(gap));
 96     memset(cur,0,sizeof(cur));
 97     int i;
 98     for(i=0; i<=N; i++)
 99     {
100         gap[deep[i]] ++;
101     }
102     int begin = s;
103     while(deep[s] < N)
104     {
105         if(begin == t)
106         {
107             flow += Augment(s,t);
108             begin = s;
109         }
110         bool ok = false;
111         int i;
112         for(i=cur[begin]; i<G[begin].size(); i++)
113         {
114             Edge& e = edge[G[begin][i]];
115             if(e.cap > e.flow && deep[begin] == deep[e.to] + 1)
116             {
117                 ok = true;
118                 front[e.to] = G[begin][i];
119                 cur[begin] = i;
120                 begin = e.to;
121                 break;
122             }
123         }
124         if(!ok)
125         {
126             int m = N - 1;
127             int i;
128             for(i=0; i<G[begin].size(); i++)
129             {
130                 Edge& e = edge[G[begin][i]];
131                 if(e.cap > e.flow)
132                 {
133                     m = min(m, deep[e.to]);
134                 }
135             }
136             if(--gap[deep[begin]] == 0)
137             {
138                 break;
139             }
140             gap[deep[begin] = m+1] ++;
141             cur[begin] = 0;
142             if(begin != s)
143             {
144                 begin = edge[front[begin]].from;
145             }
146         }
147     }
148     return flow;
149 }
150 
151 int main()
152 {
153     int T;
154     scanf("%d",&T);
155     int Case;
156     for(Case=1; Case<=T; Case++)
157     {
158         scanf("%d%d",&N,&M);
159         int i;
160         for(i=0; i<=N; i++)
161         {
162             G[i].clear();
163         }
164         cnt = 0;
165         memset(deep,0,sizeof(deep));
166         for(i=0; i<M; i++)
167         {
168             int from;
169             int to;
170             int cap;
171             scanf("%d%d%d",&from,&to,&cap);
172             addEdge(from,to,cap);
173         }
174         int flow = Maxflow(1,N);
175         printf("Case %d: %d\n",Case,flow);
176     }
177     return 0;
178 }

View Code

 

转载于:https://www.cnblogs.com/pcpcpc/p/3301956.html