Problem p00257 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"
#include <unordered_map>
#include <unordered_set>
#pragma warning(disable : 4996)
using namespace std;
using ld = long double;
template <class T> using Table = vector<vector<T>>;
const ld eps = 1e-9;

// < "D:\D_Download\Visual Studio
// 2015\Projects\programing_contest_c++\Debug\a.txt"

typedef int Weight;
struct Edge {
  int src, dst;
  Weight weight;
  Edge(int src, int dst, Weight weight) : src(src), dst(dst), weight(weight) {}
};
struct Dscc {
public:
  // belongs,newedges
  pair<vector<vector<int>>, vector<vector<int>>>
  get(const vector<vector<int>> &edges) {
    nums.resize(edges.size());
    fill(nums.begin(), nums.end(), -1);
    vector<vector<int>> revedges(edges.size());
    for (int i = 0; i < edges.size(); ++i) {
      for (auto j : edges[i]) {
        revedges[j].push_back(i);
      }
    }
    int num = 0;
    for (int i = 0; i < edges.size(); ++i) {
      dfs(i, num, edges);
    }
    vector<int> big(nums.size());
    for (int i = 0; i < nums.size(); ++i) {
      big[nums[i]] = i;
    }
    reverse(big.begin(), big.end());
    unis.resize(edges.size());
    fill(unis.begin(), unis.end(), -1);
    num = 0;
    for (int i = 0; i < big.size(); ++i) {

      dfs2(big[i], num, revedges);
      num++;
    }
    vector<int> nums;
    for (int i = 0; i < unis.size(); ++i) {
      nums.push_back(unis[i]);
    }
    sort(nums.begin(), nums.end());
    nums.erase(unique(nums.begin(), nums.end()), nums.end());

    map<int, int> mp;
    for (int i = 0; i < nums.size(); ++i) {
      mp[nums[i]] = i;
    }
    for (int i = 0; i < unis.size(); ++i) {
      unis[i] = mp[unis[i]];
    }

    vector<vector<int>> belongs(nums.size());
    for (int i = 0; i < unis.size(); ++i) {
      belongs[unis[i]].push_back(i);
    }
    vector<vector<int>> newedges(nums.size());
    for (int i = 0; i < edges.size(); ++i) {
      for (auto j : edges[i]) {
        if (unis[i] != unis[j]) {
          newedges[unis[i]].push_back(unis[j]);
        }
      }
    }
    return make_pair(belongs, newedges);
  }

  // belongs,newedges
  pair<vector<vector<int>>, vector<vector<Edge>>>
  get(const vector<vector<Edge>> &edges) {
    const int old_node_size = edges.size();
    nums.resize(old_node_size);
    fill(nums.begin(), nums.end(), -1);
    vector<vector<Edge>> revedges(old_node_size);
    for (const auto &e : edges) {
      for (const auto &j : e) {
        revedges[j.dst].push_back(Edge(j.dst, j.src, j.weight));
      }
    }
    int num = 0;
    for (int i = 0; i < old_node_size; ++i) {
      dfs(i, num, edges);
    }
    vector<int> big(old_node_size);
    for (int i = 0; i < old_node_size; ++i) {
      big[nums[i]] = i;
    }
    reverse(big.begin(), big.end());

    unis.resize(old_node_size);
    fill(unis.begin(), unis.end(), -1);

    num = 0;
    for (int i = 0; i < old_node_size; ++i) {
      dfs2(big[i], num, revedges);
      num++;
    }
    vector<int> nums;
    for (int i = 0; i < old_node_size; ++i) {
      nums.push_back(unis[i]);
    }

    sort(nums.begin(), nums.end());
    nums.erase(unique(nums.begin(), nums.end()), nums.end());
    const int new_node_size = nums.size();

    map<int, int> mp;
    for (int i = 0; i < new_node_size; ++i) {
      mp[nums[i]] = i;
    }
    for (int i = 0; i < old_node_size; ++i) {
      unis[i] = mp[unis[i]];
    }

    vector<vector<int>> belongs(new_node_size);
    for (int i = 0; i < old_node_size; ++i) {
      belongs[unis[i]].push_back(i);
    }
    vector<vector<Edge>> newedges(new_node_size);
    for (const auto &e : edges) {
      for (const auto &j : e) {
        if (unis[j.src] != unis[j.dst]) {
          newedges[unis[j.src]].push_back(
              Edge(unis[j.src], unis[j.dst], j.weight));
        }
      }
    }
    return make_pair(belongs, newedges);
  }

private:
  vector<int> nums;
  vector<int> unis;

  void dfs(const int id, int &num, const vector<vector<int>> &edges) {
    if (nums[id] != -1)
      return;
    else {
      nums[id] = -2;
      for (auto i : edges[id]) {
        dfs(i, num, edges);
      }
    }
    nums[id] = num++;
    return;
  }
  void dfs2(const int id, const int &num, const vector<vector<int>> &edges) {
    if (unis[id] != -1)
      return;
    else {
      unis[id] = -2;
      for (auto i : edges[id])
        dfs2(i, num, edges);
    }
    unis[id] = num;
    return;
  }
  void dfs(const int id, int &num, const vector<vector<Edge>> &edges) {
    if (nums[id] != -1)
      return;
    else {
      nums[id] = -2;
      for (auto i : edges[id]) {
        dfs(i.dst, num, edges);
      }
    }
    nums[id] = num++;
    return;
  }
  void dfs2(const int id, const int &num, const vector<vector<Edge>> &edges) {
    if (unis[id] != -1)
      return;
    else {
      unis[id] = -2;
      for (auto i : edges[id]) {
        dfs2(i.dst, num, edges);
      }
    }
    unis[id] = num;
    return;
  }

} dscc;
int come[300];
bool dfs(const int now, const vector<vector<int>> &edges, const int goal) {
  assert(come[now] == false);
  come[now] = true;
  if (now == goal)
    return true;
  else {
    if (edges[now].empty())
      return false;
    for (auto e : edges[now]) {
      if (e == now)
        assert(false);
      if (!dfs(e, edges, goal))
        return false;
    }
    return true;
  }
}
int main() {
  while (1) {
    memset(come, false, sizeof(come));
    int amax;
    cin >> amax;
    if (!amax)
      break;
    int N;
    cin >> N;
    const int goal = N + 1;
    const int start = 0;
    vector<int> ds(goal + 1);
    for (int i = 0; i < N; ++i) {
      cin >> ds[i + 1];
    }
    vector<vector<int>> edges(N + 2);
    for (int i = 0; i < N + 1; ++i) {
      for (int j = 1; j <= amax; ++j) {
        int next;
        if (i + j >= goal) {
          next = goal;
        } else {
          if (i + j + ds[i + j] >= goal) {
            next = goal;
          } else if (i + j + ds[i + j] < 0) {
            next = 0;
          } else {
            next = i + j + ds[i + j];
          }
        }
        if (find(edges[i].begin(), edges[i].end(), next) == edges[i].end()) {
          edges[i].push_back(next);
        }
        sort(edges[i].begin(), edges[i].end());
      }
    }
    auto p = dscc.get(edges);
    int newstart = -1;
    int newgoal = -1;
    for (int i = 0; i < p.first.size(); ++i) {
      auto b = p.first[i];
      if (find(b.begin(), b.end(), 0) != b.end()) {
        newstart = i;
      }
      if (find(b.begin(), b.end(), goal) != b.end()) {
        newgoal = i;
      }
    }
    if (newstart == -1 || newgoal == -1)
      cout << "ff";
    auto newedges = p.second;

    bool ans = dfs(newstart, newedges, newgoal);
    if (ans) {
      cout << "OK" << endl;
    } else {
      cout << "NG" << endl;
    }
  }
  return 0;
}

Fixed submission:
#include "bits/stdc++.h"
#include <unordered_map>
#include <unordered_set>
#pragma warning(disable : 4996)
using namespace std;
using ld = long double;
template <class T> using Table = vector<vector<T>>;
const ld eps = 1e-9;

// < "D:\D_Download\Visual Studio
// 2015\Projects\programing_contest_c++\Debug\a.txt"

typedef int Weight;
struct Edge {
  int src, dst;
  Weight weight;
  Edge(int src, int dst, Weight weight) : src(src), dst(dst), weight(weight) {}
};
struct Dscc {
public:
  // belongs,newedges
  pair<vector<vector<int>>, vector<vector<int>>>
  get(const vector<vector<int>> &edges) {
    nums.resize(edges.size());
    fill(nums.begin(), nums.end(), -1);
    vector<vector<int>> revedges(edges.size());
    for (int i = 0; i < edges.size(); ++i) {
      for (auto j : edges[i]) {
        revedges[j].push_back(i);
      }
    }
    int num = 0;
    for (int i = 0; i < edges.size(); ++i) {
      dfs(i, num, edges);
    }
    vector<int> big(nums.size());
    for (int i = 0; i < nums.size(); ++i) {
      big[nums[i]] = i;
    }
    reverse(big.begin(), big.end());
    unis.resize(edges.size());
    fill(unis.begin(), unis.end(), -1);
    num = 0;
    for (int i = 0; i < big.size(); ++i) {

      dfs2(big[i], num, revedges);
      num++;
    }
    vector<int> nums;
    for (int i = 0; i < unis.size(); ++i) {
      nums.push_back(unis[i]);
    }
    sort(nums.begin(), nums.end());
    nums.erase(unique(nums.begin(), nums.end()), nums.end());

    map<int, int> mp;
    for (int i = 0; i < nums.size(); ++i) {
      mp[nums[i]] = i;
    }
    for (int i = 0; i < unis.size(); ++i) {
      unis[i] = mp[unis[i]];
    }

    vector<vector<int>> belongs(nums.size());
    for (int i = 0; i < unis.size(); ++i) {
      belongs[unis[i]].push_back(i);
    }
    vector<vector<int>> newedges(nums.size());
    for (int i = 0; i < edges.size(); ++i) {
      for (auto j : edges[i]) {
        if (unis[i] != unis[j]) {
          newedges[unis[i]].push_back(unis[j]);
        }
      }
    }
    return make_pair(belongs, newedges);
  }

  // belongs,newedges
  pair<vector<vector<int>>, vector<vector<Edge>>>
  get(const vector<vector<Edge>> &edges) {
    const int old_node_size = edges.size();
    nums.resize(old_node_size);
    fill(nums.begin(), nums.end(), -1);
    vector<vector<Edge>> revedges(old_node_size);
    for (const auto &e : edges) {
      for (const auto &j : e) {
        revedges[j.dst].push_back(Edge(j.dst, j.src, j.weight));
      }
    }
    int num = 0;
    for (int i = 0; i < old_node_size; ++i) {
      dfs(i, num, edges);
    }
    vector<int> big(old_node_size);
    for (int i = 0; i < old_node_size; ++i) {
      big[nums[i]] = i;
    }
    reverse(big.begin(), big.end());

    unis.resize(old_node_size);
    fill(unis.begin(), unis.end(), -1);

    num = 0;
    for (int i = 0; i < old_node_size; ++i) {
      dfs2(big[i], num, revedges);
      num++;
    }
    vector<int> nums;
    for (int i = 0; i < old_node_size; ++i) {
      nums.push_back(unis[i]);
    }

    sort(nums.begin(), nums.end());
    nums.erase(unique(nums.begin(), nums.end()), nums.end());
    const int new_node_size = nums.size();

    map<int, int> mp;
    for (int i = 0; i < new_node_size; ++i) {
      mp[nums[i]] = i;
    }
    for (int i = 0; i < old_node_size; ++i) {
      unis[i] = mp[unis[i]];
    }

    vector<vector<int>> belongs(new_node_size);
    for (int i = 0; i < old_node_size; ++i) {
      belongs[unis[i]].push_back(i);
    }
    vector<vector<Edge>> newedges(new_node_size);
    for (const auto &e : edges) {
      for (const auto &j : e) {
        if (unis[j.src] != unis[j.dst]) {
          newedges[unis[j.src]].push_back(
              Edge(unis[j.src], unis[j.dst], j.weight));
        }
      }
    }
    return make_pair(belongs, newedges);
  }

private:
  vector<int> nums;
  vector<int> unis;

  void dfs(const int id, int &num, const vector<vector<int>> &edges) {
    if (nums[id] != -1)
      return;
    else {
      nums[id] = -2;
      for (auto i : edges[id]) {
        dfs(i, num, edges);
      }
    }
    nums[id] = num++;
    return;
  }
  void dfs2(const int id, const int &num, const vector<vector<int>> &edges) {
    if (unis[id] != -1)
      return;
    else {
      unis[id] = -2;
      for (auto i : edges[id])
        dfs2(i, num, edges);
    }
    unis[id] = num;
    return;
  }
  void dfs(const int id, int &num, const vector<vector<Edge>> &edges) {
    if (nums[id] != -1)
      return;
    else {
      nums[id] = -2;
      for (auto i : edges[id]) {
        dfs(i.dst, num, edges);
      }
    }
    nums[id] = num++;
    return;
  }
  void dfs2(const int id, const int &num, const vector<vector<Edge>> &edges) {
    if (unis[id] != -1)
      return;
    else {
      unis[id] = -2;
      for (auto i : edges[id]) {
        dfs2(i.dst, num, edges);
      }
    }
    unis[id] = num;
    return;
  }

} dscc;
int come[300];
bool dfs(const int now, const vector<vector<int>> &edges, const int goal) {
  if (come[now])
    return true;
  come[now] = true;
  if (now == goal)
    return true;
  else {
    if (edges[now].empty())
      return false;
    for (auto e : edges[now]) {
      if (e == now)
        assert(false);
      if (!dfs(e, edges, goal))
        return false;
    }
    return true;
  }
}
int main() {
  while (1) {
    memset(come, false, sizeof(come));
    int amax;
    cin >> amax;
    if (!amax)
      break;
    int N;
    cin >> N;
    const int goal = N + 1;
    const int start = 0;
    vector<int> ds(goal + 1);
    for (int i = 0; i < N; ++i) {
      cin >> ds[i + 1];
    }
    vector<vector<int>> edges(N + 2);
    for (int i = 0; i < N + 1; ++i) {
      for (int j = 1; j <= amax; ++j) {
        int next;
        if (i + j >= goal) {
          next = goal;
        } else {
          if (i + j + ds[i + j] >= goal) {
            next = goal;
          } else if (i + j + ds[i + j] < 0) {
            next = 0;
          } else {
            next = i + j + ds[i + j];
          }
        }
        if (find(edges[i].begin(), edges[i].end(), next) == edges[i].end()) {
          edges[i].push_back(next);
        }
        sort(edges[i].begin(), edges[i].end());
      }
    }
    auto p = dscc.get(edges);
    int newstart = -1;
    int newgoal = -1;
    for (int i = 0; i < p.first.size(); ++i) {
      auto b = p.first[i];
      if (find(b.begin(), b.end(), 0) != b.end()) {
        newstart = i;
      }
      if (find(b.begin(), b.end(), goal) != b.end()) {
        newgoal = i;
      }
    }
    if (newstart == -1 || newgoal == -1)
      cout << "ff";
    auto newedges = p.second;

    bool ans = dfs(newstart, newedges, newgoal);
    if (ans) {
      cout << "OK" << endl;
    } else {
      cout << "NG" << endl;
    }
  }
  return 0;
}