Drainage Ditches（dinic）

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<queue>
 4 #include<algorithm>
 5 using namespace std;
 6 const int M = 210 , inf = 0x3f3f3f3f ;
 7 int m , n ;
 8 int map[M][M] ;
 9 int dis[M];
10 
11 bool bfs ()
12 {
13     queue <int> q ;
14     while (!q.empty ())
15         q.pop () ;
16     memset (dis , 0xff , sizeof(dis)) ;
17     dis[1] = 0 ;
18     q.push (1) ;
19     while (!q.empty () ) {
20         int u = q.front () ;
21         q.pop () ;
22         for (int v = 1 ; v <= n ; v++) {
23             if (map[u][v] && dis[v] == -1) {
24                 dis[v] = dis[u] + 1 ;
25                 q.push (v) ;
26             }
27         }
28     }
29     if (dis[n] > 0)
30         return true ;
31     return false ;
32 }
33 
34 int find (int u , int low)
35 {
36     int a = 0 ;
37     if (u == n)
38         return low ;
39     for (int v = 1 ; v <= n ; v++) {
40         if (map[u][v] && dis[v] == dis[u] + 1 && (a = find (v , min(map[u][v] , low)))) {
41             map[u][v] -= a ;
42             map[v][u] += a ;
43             return a ;
44         }
45     }
46     return 0 ;
47 }
48 
49 int main ()
50 {
51  //   freopen ("a.txt" , "r" , stdin) ;
52     int u , v , w ;
53     int ans ;
54     while (~ scanf ("%d%d" , &m , &n)) {
55         memset (map , 0 , sizeof(map)) ;
56       //  printf ("m = %d , n = %d\n" , m , n) ;
57         while (m--) {
58             scanf ("%d%d%d" , &u , &v , &w) ;
59             map[u][v] += w ;
60         }
61         int maxn = 0 ;
62         while (bfs()) {
63             if (ans = find(1 , inf))
64                 maxn += ans ;
65         }
66         printf ("%d\n" , maxn) ;
67     }
68     return 0 ;
69 }