pku1273 Drainage Ditches

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

网络流，Dinic

 #include <stdio.h>
 #include <string.h>
 #include <queue>

 using namespace std;

 const int inf = <<;
 const int maxn = , maxm = ;

 struct Edge
 {
     int v, f, nxt;
 };

 int n, src, sink;
 int g[maxn + ];
 int nume;
 Edge e[maxm* + ];

 void addedge(int u, int v, int c)
 {
     e[++nume].v = v;
     e[nume].f = c;
     e[nume].nxt = g[u];
     g[u] = nume;
     e[++nume].v = u;
     e[nume].nxt = g[v];
     g[v] = nume;
 }

 queue<int> que;
 bool vis[maxn + ];
 int dist[maxn + ];

 void bfs()
 {
     memset(dist, , sizeof(dist));
     while(!que.empty())
     {
         que.pop();
     }
     vis[src] = true;
     que.push(src);
     while(!que.empty())
     {
         int u = que.front();
         que.pop();
         for(int i=g[u]; i; i=e[i].nxt)
         {
             if(e[i].f && !vis[e[i].v])
             {
                 que.push(e[i].v);
                 dist[e[i].v] = dist[u] + ;
                 vis[e[i].v] = true;
             }
         }
     }
 }

 int dfs(int u, int delta)
 {
     if(u == sink)
     {
         return delta;
     }
     else
     {
         int ret = ;
         for(int i=g[u]; delta && i; i=e[i].nxt)
         {
             if(e[i].f && dist[e[i].v] == dist[u] + )
             {
                 int dd = dfs(e[i].v, min(e[i].f, delta));
                 e[i].f -= dd;
                 e[i ^ ].f += dd;
                 delta -= dd;
                 ret += dd;
             }
         }
         return ret;
     }
 }

 int maxflow()
 {
     int ret = ;
     while(true)
     {
         memset(vis, , sizeof(vis));
         bfs();
         if(!vis[sink])
         {
             return ret;
         }
         ret += dfs(src, inf);
     }
 }

 int main()
 {
     int n, m;
     int i, x, y, z;
     while(~scanf("%d%d", &m, &n))
     {
         memset(g, , sizeof(g));
         nume = ;
         src = ;
         sink = n;
         for(i=; i<=m; i++)
         {
             scanf("%d%d%d", &x, &y, &z);
             addedge(x, y, z);
         }
         x = maxflow();
         printf("%d\n", x);
     }
     return ;
 }