Cogs 12 运输问题2 （有上下界网络流）

 #include <cstdlib>
 #include <algorithm>
 #include <cstring>
 #include <iostream>
 #include <cstdio>
 #include <vector>
 
 using namespace std;
 
 const int N =  +  ;
 const int oo = 0x3f3f3f3f;
 
 struct Edge {
   int from, to, cap, flow;
 };
 
 struct Dinic {
   int n, m, s, t;
   int dis[N], cur[N], que[N << ];
   bool vis[N];
   vector <Edge> edges;
   vector <int> G[N];
 
   void add(int from, int to, int cap) {
     edges.push_back((Edge) {from, to, cap, });
     edges.push_back((Edge) {to, from, , });
     m = edges.size();
     G[from].push_back(m - );
     G[to].push_back(m - );
   }
 
   bool bfs() {
     int head = , tail = ;
 
     memset(vis, false, sizeof vis);
     dis[s] = ; vis[s] = true; que[head] = s;
     while(head <= tail) {
       int x = que[head];
 
       for(int i = ; i < (signed) G[x].size(); ++ i) {
         Edge &e = edges[G[x][i]];
 
         if(!vis[e.to] && e.cap > e.flow) {
           vis[e.to] = true;
           dis[e.to] = dis[x] + ;
           que[++ tail] = e.to;
         }
       }
       ++ head;
     }
     return vis[t];
   }
 
   int dfs(int x, int a) {
     if(x == t || a == ) return a;
 
     int flw = , f;
 
     for(int &i = cur[x]; i < (signed) G[x].size(); ++ i) {
       Edge &e = edges[G[x][i]];
 
       if(dis[e.to] == dis[x] +  && (f = dfs(e.to, min(a, e.cap - e.flow))) > ) {
         e.flow += f; edges[G[x][i] ^ ].flow -= f; flw += f; a -= f;
         if(a == ) break;
       }
     }
     return flw;
   }
 
   int MaxFlow(int s, int t) {
     this->s = s; this->t = t;
 
     int flw = ;
 
     while(bfs()) {
       memset(cur, , sizeof cur);
       flw += dfs(s, oo);
     }
     return flw;
   }
 }net;
 
 int n, M[N];
 
 int main() {
 #ifndef ONLINE_JUDGE
   freopen("maxflowb.in", "r", stdin);
   freopen("maxflowb.out", "w", stdout);
 #endif
 
   int Up, Down;
 
   scanf("%d", &n); net.n = n + ;
   for(int i = ; i <= n; ++ i) {
     for(int j = ; j <= n; ++ j) {
       scanf("%d%d", &Down, &Up);
       M[i] -= Down; M[j] += Down;
       net.add(i, j, Up - Down);
     }
   }
   net.add(n, , oo);
   for(int i = ; i <= n; ++ i) {
     if(M[i] > ) {
       net.add(, i, M[i]);
     }
     else if(M[i] < ){
       net.add(i, n + , -M[i]);
     }
   }
   net.MaxFlow(, n + );
   printf("%d\n", net.MaxFlow(, n));
 
 #ifndef ONLINE_JUDGE
   fclose(stdin); fclose(stdout);
 #endif
   return ;
 }

Cogs 12

连边方式见图。