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 = 100 +  5;
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 << 1];
  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, 0});
    edges.push_back((Edge) {to, from, 0, 0});
    m = edges.size();
    G[from].push_back(m - 2);
    G[to].push_back(m - 1);
  }

  bool bfs() {
    int head = 1, tail = 1;

    memset(vis, false, sizeof vis);
    dis[s] = 0; vis[s] = true; que[head] = s;
    while(head <= tail) {
      int x = que[head];

      for(int i = 0; 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] + 1;
          que[++ tail] = e.to;
        }
      }
      ++ head;
    }
    return vis[t];
  }

  int dfs(int x, int a) {
    if(x == t || a == 0) return a;

    int flw = 0, f;

    for(int &i = cur[x]; i < (signed) G[x].size(); ++ i) {
      Edge &e = edges[G[x][i]];
      
      if(dis[e.to] == dis[x] + 1 && (f = dfs(e.to, min(a, e.cap - e.flow))) > 0) {
        e.flow += f; edges[G[x][i] ^ 1].flow -= f; flw += f; a -= f;
        if(a == 0) break;
      }
    }
    return flw;
  }

  int MaxFlow(int s, int t) {
    this->s = s; this->t = t;

    int flw = 0;

    while(bfs()) {
      memset(cur, 0, 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 + 1;
  for(int i = 1; i <= n; ++ i) {
    for(int j = 1; j <= n; ++ j) {
      scanf("%d%d", &Down, &Up);
      M[i] -= Down; M[j] += Down;
      net.add(i, j, Up - Down);
    }
  }
  net.add(n, 1, oo);
  for(int i = 1; i <= n; ++ i) {
    if(M[i] > 0) {
      net.add(0, i, M[i]);
    }
    else if(M[i] < 0){
      net.add(i, n + 1, -M[i]);
    }
  }
  net.MaxFlow(0, n + 1);
  printf("%d
", net.MaxFlow(1, n));
  
#ifndef ONLINE_JUDGE
  fclose(stdin); fclose(stdout);
#endif
  return 0;
}

连边方式见图。