POJ-1273 Drainage Ditches (网络流入门题)

 1 #include "bits/stdc++.h"
 2 using namespace std;
 3 typedef long long LL;
 4 const int MAX=205;
 5 int n,m,s,t;
 6 int tot,head[MAX],adj[MAX<<1],wei[MAX<<1],next[MAX<<1];
 7 int cur[MAX],deep[MAX];
 8 void addedge(int u,int v,int w){
 9     tot++;adj[tot]=v,wei[tot]=w,next[tot]=head[u],head[u]=tot;
10 }
11 bool bfs(){
12     int i,j;
13     memset(deep,127,sizeof(deep));
14     deep[s]=0;
15     queue <int> q; q.push(s);
16     while (!q.empty()){
17         int u=q.front();q.pop();
18         for (i=head[u];i;i=next[i]){
19             if (deep[adj[i]]>1e9 && wei[i]>0){
20                 deep[adj[i]]=deep[u]+1;
21                 q.push(adj[i]);
22             }
23         }
24     }
25     return deep[t]<1e9;
26 }
27 int dfs(int x,int flo){
28     if (x==t || flo==0) return flo;
29     int j;
30     for (int &i=cur[x];i;i=next[i]){
31         if (deep[adj[i]]==deep[x]+1 && wei[i]>0){
32             j=dfs(adj[i],min(flo,wei[i]));
33             if (j){
34                 wei[i]-=j;
35                 wei[i^1]+=j;
36                 return j;
37             }
38         }
39     }
40     return 0;
41 }
42 int main(){
43     freopen ("ditches.in","r",stdin);freopen ("ditches.out","w",stdout);
44     int i,j,u,v,w;
45     while (~scanf("%d%d",&m,&n)){
46         tot=1;s=1,t=n;
47         memset(head,0,sizeof(head));
48         for (i=1;i<=m;i++){
49             scanf("%d%d%d",&u,&v,&w);
50             addedge(u,v,w),addedge(v,u,0);
51         }
52         int flow=0,dd;
53         while (bfs()){
54             for (i=1;i<=n;i++) cur[i]=head[i];
55             while (dd=dfs(s,1e9)) flow+=dd;
56         }
57         printf("%d\n",flow);
58     }
59     return 0;
60 }