学步园

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>
#include <list>
#include <stack>
 
using namespace std;
 
const int kMaxN = 3001;
 
class Graph {
 public:
  Graph(int vertex_count = 0) {
    vertex_count_ = vertex_count;
    memset(degree_, 0, sizeof(degree_));
  }
  void insert_edge(int v, int w) {
    graph_[v].push_back(w);
    degree_[w]++;
  }
  void TarjanInit() {
    tarjan_count = 0;
    memset(tarjan_dfn, 0, sizeof(tarjan_dfn));
    memset(tarjan_low, 0, sizeof(tarjan_low));
    memset(tarjan_instack, false, sizeof(tarjan_instack));
    for (int i = 1; i <= vertex_count_; i++) {
      tarjan_set[i] = i;
    }
  }
  void Tarjan(int v) {                  // Need TarjanInit()
    tarjan_count++;
    tarjan_dfn[v] = tarjan_count;
    tarjan_low[v] = tarjan_count;
    tarjan_stack.push(v);
    tarjan_instack[v] = true;
 
    for (list<int>::const_iterator i = graph_[v].begin(); i != graph_[v].end(); ++i) {
      if (!tarjan_dfn[*i]) {
        Tarjan(*i);
        tarjan_low[v] = min(tarjan_low[v], tarjan_low[*i]);
      } else if (tarjan_instack[*i]) {
        tarjan_low[v] = min(tarjan_low[v], tarjan_dfn[*i]);
      }
    }
 
    if (tarjan_dfn[v] == tarjan_low[v]) {
      while (tarjan_stack.top() != v) {
        tarjan_instack[tarjan_stack.top()] = false;
        tarjan_set[tarjan_stack.top()] = v;
        tarjan_stack.pop();
      }
      tarjan_instack[tarjan_stack.top()] = false;
      tarjan_set[tarjan_stack.top()] = v;
      tarjan_stack.pop();
    }
  }
  static bool compare(const int &a, const int &b) {
    return a < b;
  }
  void unique() {
    for (int v = 0; v < vertex_count_; v++) {
      graph_[v].sort(compare);
      graph_[v].unique();
    }
  }
  void BuildDAG(Graph &new_graph) {
    for (int v = 1; v <= vertex_count_; v++) {
      for (list<int>::const_iterator i = graph_[v].begin(); i != graph_[v].end(); ++i) {
        if (tarjan_set[v] == tarjan_set[*i]) {
          continue;
        } else {
          new_graph.insert_edge(tarjan_set[v], tarjan_set[*i]);
        }
      }
    }
    new_graph.unique();
  }
  int view_degree(int v) {
    return degree_[v];
  }
 
  void show(int v) {
    cout << "Vertex " << v << " : ";
    for (list<int>::const_iterator i = graph_[v].begin(); i != graph_[v].end(); ++i) {
      cout << *i << " ";
    }
    cout << endl;
  }
  void show_all() {
    for (int i = 1; i <= vertex_count_; i++) {
      show(i);
    }
  }
 
  int tarjan_count;
  int tarjan_set[kMaxN];
  int tarjan_dfn[kMaxN];
  int tarjan_low[kMaxN];
  bool tarjan_instack[kMaxN];
  stack<int> tarjan_stack;
 private:
  int vertex_count_;
  int degree_[kMaxN];
  list<int> graph_[kMaxN];
};
 
int n, p, r;
int buy[kMaxN];
 
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  Graph graph(n);
  Graph graph_dag(n);
  cin >> r;
  for (int i = 1; i <= r; i++) {
    int x, y;
    cin >> x >> y;
    graph.insert_edge(x, y);
  }
 
  graph.TarjanInit();
  for (int i = 1; i <= n; i++) {
    if (!graph.tarjan_dfn[i]) {
      graph.Tarjan(i);
    }
  }
  graph.BuildDAG(graph_dag);
 
  graph_dag.show_all();
 
  return 0;
}