pku1273 Drainage Ditches

http://poj.org/problem?id=1273

网络流，Dinic

  1 #include <stdio.h>
  2 #include <string.h>
  3 #include <queue>
  4 
  5 using namespace std;
  6 
  7 const int inf = 1<<30;
  8 const int maxn = 202, maxm = 202;
  9 
 10 struct Edge
 11 {
 12     int v, f, nxt;
 13 };
 14 
 15 int n, src, sink;
 16 int g[maxn + 10];
 17 int nume;
 18 Edge e[maxm*2 + 10];
 19 
 20 void addedge(int u, int v, int c)
 21 {
 22     e[++nume].v = v;
 23     e[nume].f = c;
 24     e[nume].nxt = g[u];
 25     g[u] = nume;
 26     e[++nume].v = u;
 27     e[nume].nxt = g[v];
 28     g[v] = nume;
 29 }
 30 
 31 
 32 queue<int> que;
 33 bool vis[maxn + 10];
 34 int dist[maxn + 10];
 35 
 36 void bfs()
 37 {
 38     memset(dist, 0, sizeof(dist));
 39     while(!que.empty())
 40     {
 41         que.pop();
 42     }
 43     vis[src] = true;
 44     que.push(src);
 45     while(!que.empty())
 46     {
 47         int u = que.front();
 48         que.pop();
 49         for(int i=g[u]; i; i=e[i].nxt)
 50         {
 51             if(e[i].f && !vis[e[i].v])
 52             {
 53                 que.push(e[i].v);
 54                 dist[e[i].v] = dist[u] + 1;
 55                 vis[e[i].v] = true;
 56             }
 57         }
 58     } 
 59 }
 60 
 61 int dfs(int u, int delta)
 62 {
 63     if(u == sink)
 64     {
 65         return delta;
 66     } 
 67     else
 68     {
 69         int ret = 0;
 70         for(int i=g[u]; delta && i; i=e[i].nxt)
 71         {
 72             if(e[i].f && dist[e[i].v] == dist[u] + 1)
 73             {
 74                 int dd = dfs(e[i].v, min(e[i].f, delta));
 75                 e[i].f -= dd;
 76                 e[i ^ 1].f += dd;
 77                 delta -= dd;
 78                 ret += dd;
 79             }
 80         }
 81         return ret;
 82     }
 83 }
 84 
 85 int maxflow()
 86 {
 87     int ret = 0;
 88     while(true)
 89     {
 90         memset(vis, 0, sizeof(vis));
 91         bfs();
 92         if(!vis[sink])
 93         {
 94             return ret;
 95         }
 96         ret += dfs(src, inf);
 97     } 
 98 }
 99 
100 
101 int main()
102 {
103     int n, m;
104     int i, x, y, z;
105     while(~scanf("%d%d", &m, &n))
106     {
107         memset(g, 0, sizeof(g));
108         nume = 1;
109         src = 1;
110         sink = n;
111         for(i=1; i<=m; i++)
112         {
113             scanf("%d%d%d", &x, &y, &z);
114             addedge(x, y, z);
115         }
116         x = maxflow();
117         printf("%d\n", x);
118     }
119     return 0;
120 }

 

posted @ 2013-08-04 18:24  Yuan1991  阅读(141)  评论(0)  编辑  收藏  举报