FordFulkerson

FordFulkerson.cpp

// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_6_A

#include <vector>
#include <iostream>
#include <algorithm>

class FordFulkerson {
  struct edge { int from, to, cap, rev; };
  static const int INF = 1 << 30;

private:
  int n;
  std::vector<std::vector<edge> > G; // adj list
  std::vector<bool> used;

public:
  FordFulkerson (int n) : n(n), G(n) {}

  void addEdge(int from, int to, int cap) {
    G[from].push_back((edge){from, to, cap, static_cast<int>(G[to].size())});
    G[to].push_back((edge){to, from, 0, static_cast<int>(G[from].size()) - 1});
  }

  int dfs(int v, int t, int f) {
      if (v == t) return f;
      used[v] = true;
      for (int i = 0; i < G[v].size(); i++) {
          edge &e = G[v][i];
          if (!used[e.to] && e.cap > 0) {
              int d = dfs(e.to, t, std::min(f, e.cap));
              if (d > 0) {
                  e.cap -= d;
                  G[e.to][e.rev].cap += d;
                  return d;
              }
          }
      }
      return 0;
  }

  int calc(int s, int t) {
      int flow = 0;
      while (true) {
          used.clear();
          used.resize(n, false);
          int f = dfs(s, t, INF);
          if (f == 0) return flow;
          flow += f;
      }
  }
};

int main() {
  int n, m;
  std::cin >> n >> m;
  FordFulkerson ff(n);
  for (int i = 0; i < m; i++) {
    int u, v, c;
    std::cin >> u >> v >> c;
    ff.addEdge(u, v, c);
  }
  std::cout << ff.calc(0, n-1) << std::endl;
}