hdu 1532 Drainage Ditches(最大流）

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cstdlib>
 6 #include<string.h>
 7 #include<set>
 8 #include<vector>
 9 #include<queue>
10 #include<stack>
11 #include<map>
12 #include<cmath>
13 typedef long long ll;
14 typedef unsigned long long LL;
15 using namespace std;
16 const double PI=acos(-1.0);
17 const double eps=0.0000000001;
18 const int INF=1e9;
19 const int N=1000+100;
20 int mp[N][N];
21 int vis[N];
22 int pre[N];
23 int m,n;
24 int BFS(int s,int t){
25     queue<int>q;
26     memset(pre,-1,sizeof(pre));
27     memset(vis,0,sizeof(vis));
28     pre[s]=0;
29     vis[s]=1;
30     q.push(s);
31     while(!q.empty()){
32         int p=q.front();
33         q.pop();
34         for(int i=1;i<=n;i++){
35             if(mp[p][i]>0&&vis[i]==0){
36                 pre[i]=p;
37                 vis[i]=1;
38                 if(i==t)return 1;
39                 q.push(i);
40             }
41         }
42     }
43     return false;
44 }
45 int EK(int s,int t){
46     int flow=0;
47     while(BFS(s,t)){
48         //BFS(s,t);
49         int dis=INF;
50         for(int i=t;i!=s;i=pre[i])
51             dis=min(mp[pre[i]][i],dis);
52         for(int i=t;i!=s;i=pre[i]){
53             mp[pre[i]][i]=mp[pre[i]][i]-dis;
54             mp[i][pre[i]]=mp[i][pre[i]]+dis;
55         }
56         flow=flow+dis;
57     }
58     return flow;
59 }
60 int main(){
61     while(scanf("%d%d",&n,&m)!=EOF){
62         memset(mp,0,sizeof(mp));
63         for(int i=0;i<n;i++){
64             int u,v,w;
65             scanf("%d%d%d",&u,&v,&w);
66             mp[u][v]=mp[u][v]+w;
67         }
68         int ans=EK(1,m);
69         cout<<ans<<endl;
70     }
71 
72 }