POJ 1273

 1 //一般增广路，每次不断在生于网络找层次网络，直到找不到说明已找到最大流量
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <queue>
 5 #include <iostream>
 6 const int N = 210;
 7 using namespace std;
 8 
 9 int n,m;
10 int cap[N][N] , flow[N][N] , lev[N];
11 int pre[N];//回溯标记
12 
13 bool find_levelnet()
14 {
15     memset(pre , -1 , sizeof(pre));
16     queue<int> q;
17     q.push(1);
18     pre[1] = 0;
19     memset(lev , 0x3f , sizeof(lev));
20     lev[1] = 1;
21     while(!q.empty()){
22         int u = q.front();
23         q.pop();
24         for(int i=1 ; i<=n ; i++){
25             int tmp = cap[u][i] - flow[u][i];
26             if(tmp && lev[i] > lev[u]+1){
27                 lev[i] = lev[u]+1;
28                 pre[i] = u;
29                 q.push(i);
30             }
31         }
32     }
33     if(lev[n] > n) return false;
34     return true;
35 }
36 
37 int get_min_flow()
38 {
39     int minn = 0x3f3f3f3f;
40     for(int i = n ; i!=1 ; i=pre[i]){
41         int u = pre[i];
42         minn = min(minn , cap[u][i] - flow[u][i]);
43     }
44     return minn;
45 }
46 
47 void update(int d)
48 {
49     for(int i = n ; i!=1 ; i=pre[i]){
50         int u = pre[i];
51         flow[u][i] += d;
52         flow[i][u] -= d;
53     }
54 }
55 
56 int main()
57 {
58     //freopen("a.in","rb",stdin);
59     int u,v,d;
60     while(scanf("%d%d" , &m , &n) == 2){
61         memset(cap , 0 ,sizeof(cap));
62         memset(flow , 0 ,sizeof(flow));
63         for(int i=0 ; i<m ; i++){
64             scanf("%d%d%d" , &u , &v , &d);
65             cap[u][v] += d; //可能有重边不断叠加
66         }
67 
68         int ans = 0;
69         while(find_levelnet()){
70             int min_flow = get_min_flow();
71             ans += min_flow;
72             update(min_flow);
73         }
74 
75         printf("%d\n",ans);
76     }
77     return 0;
78 }