POJ 1273 Drainage Ditches【最大流】

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring> 
 4 #include <cmath> 
 5 #include<stack>
 6 #include<vector>
 7 #include<map> 
 8 #include<set>
 9 #include<queue> 
10 #include<algorithm>  
11 using namespace std;
12 
13 typedef long long LL;
14 const int INF = (1<<30)-1;
15 const int mod=1000000007;
16 const int maxn=10005;
17 int n,m,M;
18 
19 struct Edge{
20     int from,to,cap,flow;
21     Edge(int u,int v,int c,int f) :from(u),to(v),cap(c),flow(f) {}
22 };
23 
24 
25 vector<Edge> edges;//存边 
26 vector<int> G[maxn];//邻接表 
27 int a[maxn];//到起点i的可改进量 
28 int p[maxn];//最短 路树上p的入弧编号 
29 
30 void init(){
31     for(int i=0;i<n;i++) G[i].clear();
32     edges.clear();
33 }
34 
35 void addedges(int from,int to,int cap){
36     edges.push_back(Edge(from,to,cap,0));
37     edges.push_back(Edge(to,from,0,0));//反向弧
38     m=edges.size();
39     G[from].push_back(m-2);
40     G[to].push_back(m-1);     
41 }
42 
43 int Maxflow(int s,int t){
44     int flow=0;
45     for(;;){
46         memset(a,0,sizeof(a));
47         queue<int> q;
48         q.push(s);
49         a[s]=INF;
50         while(!q.empty()){
51             int x=q.front();q.pop();
52             for(int i = 0;i < G[x].size(); i++){
53                 Edge& e = edges[G[x][i]];
54                 if(!a[e.to]&&e.cap>e.flow){
55                     p[e.to] = G[x][i];
56                     a[e.to] = min(a[x], e.cap-e.flow);
57                     q.push(e.to);
58                 }
59             }
60             if(a[t]) break;        
61         } 
62         if(!a[t]) break;
63         for(int u = t;u !=s ;u=edges[p[u]].from){
64             edges[p[u]].flow+=a[t];
65             edges[p[u]^1].flow-=a[t];
66         }
67         flow+=a[t];
68     }
69     return flow;
70 }
71 
72 int main(){
73     while(scanf("%d %d",&M,&n)!=EOF){
74         init();
75         for(int i=0;i<M;i++){
76             int u,v,c;
77             scanf("%d %d %d",&u,&v,&c);
78             u--;v--;
79             addedges(u,v,c);    
80         }
81         printf("%d\n",Maxflow(0,n-1));
82     } 
83     return 0;
84 }