Problem p01426 (C++)

Buggy submission (status: Memory Limit Exceeded):
#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" > "D:\D_Download\Visual
///Studio 2015\Projects\programing_contest_c++\Debug\b.answer"

typedef double Weight;

struct Edge {
  int src, dst;
  Weight weight;
  int id;
  Edge(int src_, int dst_, Weight weight_, const int id_)
      : src(src_), dst(dst_), weight(weight_), id(id_) {}
  Edge(int src, int dst, Weight weight) : src(src), dst(dst), weight(weight) {}
  Edge() : src(0), dst(0), weight(0) {}
};
const Weight INF = 1e18;
const Weight ZERO = 0;
bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src
                            : e.dst < f.dst;
}
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
ld getdis(const vector<ld> &f, const vector<ld> &t) {
  ld amin = -1e9;
  ld amax = 1e9;
  int n = 100;
  while (n--) {
    ld amid0 = (amin * 2 + amax) / 3;
    ld amid1 = (amin + amax * 2) / 3;
    ld len0 = 0;
    ld len1 = 0;
    {

      for (int i = 0; i < f.size(); ++i) {
        len0 += (t[i] - amid0 * f[i]) * (t[i] - amid0 * f[i]);
      }
      for (int i = 0; i < f.size(); ++i) {
        len1 += (t[i] - amid1 * f[i]) * (t[i] - amid1 * f[i]);
      }
    }
    if (len0 < len1) {
      amax = amid1;
    } else {
      amin = amid0;
    }
    if (!n)
      return len0;
  }
}
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;

namespace getcycle {
pair<int, vector<Edge>> dfs(const Graph &g, vector<int> &used, const int now,
                            const int id) {
  if (used[now] == -1) {
    used[now] = id;
    for (auto e : g[now]) {
      if (used[e.dst] == id) {
        return make_pair(e.dst, vector<Edge>(1, e));
      } else if (used[e.dst] != -1) {
        continue;
      } else {
        assert(used[e.dst] == -1);
        auto p(dfs(g, used, e.dst, id));
        if (p.first == -1) {
          return p;
        } else if (p.first == -2) {
          continue;
        } else {
          p.second.push_back(e);
          if (p.first == now) {
            return make_pair(-1, p.second);
          } else {
            return p;
          }
        }
      }
    }
    return make_pair(-2, vector<Edge>(0));
  } else {
    assert(false);
    return make_pair(0, vector<Edge>(0));
  }
}
vector<Edge> get_cycle(const Graph &g, const int start) {
  vector<int> used(g.size(), -1);

  int id = 0;
  for (int i = 0; i < g.size(); ++i) {
    if (used[i] == -1) {

      vector<Edge> cycles = dfs(g, used, i, id).second;
      id++;
      if (!cycles.empty()) {

        reverse(cycles.begin(), cycles.end());
        return cycles;
      }
    }
  }
  return vector<Edge>(0);
}
} // namespace getcycle

// aoj2309???varify??????????????£??????????????§????????????????????????
pair<Weight, Graph> chu_liu(const Graph &g, const int start, const int e_size) {
  Graph revg(g.size());

  /*????´???°???Edge?????°????????§??????*/
  vector<Edge> memo(e_size);

  for (auto es : g) {
    for (auto e : es) {
      // memo[e.id] = e;
      revg[e.dst].emplace_back(e.dst, e.src, e.weight);
    }
  }
  Graph tree(g.size());
  ld total_len = 0;
  for (int node = 0; node < g.size(); ++node) {
    if (node == start)
      continue;
    else {
      Weight amin = INF;
      Edge min_edge;
      for (auto reve : revg[node]) {
        if (amin > reve.weight) {
          amin = reve.weight;
          min_edge = Edge(reve.dst, reve.src, reve.weight);
        }
      }
      if (amin < INF) {
        total_len += min_edge.weight;
        tree[min_edge.src].emplace_back(min_edge);
      }
    }
  }
  Weight cycle_len = 0;
  vector<Edge> cycle_edges(getcycle::get_cycle(tree, start));
  for (auto e : cycle_edges) {
    cycle_len += e.weight;
  }
  if (cycle_edges.empty()) {
    return make_pair(total_len, g);
  } else {
    vector<bool> node_is_cycle(g.size());

    /*????´???°???Edge?????°????????§??????*/
    vector<int> edge_is_cycle(g.size() * g.size());

    vector<pair<int, Weight>> prevs(g.size(), make_pair(-1, ZERO));

    for (auto ce : cycle_edges) {
      node_is_cycle[ce.src] = true;
      node_is_cycle[ce.dst] = true;
      prevs[ce.dst] = make_pair(ce.src, ce.weight);
    }
    Graph newg(g.size());
    const int compress = cycle_edges[0].src;
    int ne_size = 0;
    for (int s = 0; s < g.size(); ++s) {
      bool src_is_cycle = node_is_cycle[s];
      for (auto e : g[s]) {
        bool dst_is_cycle = node_is_cycle[e.dst];
        if (src_is_cycle && dst_is_cycle) {
        } else if (src_is_cycle) {
          newg[compress].push_back(Edge(compress, e.dst, e.weight, e.id));
          ne_size++;
        } else if (dst_is_cycle) {
          newg[s].push_back(
              Edge(s, compress, e.weight - prevs[e.dst].second, e.id));
          ne_size++;
        } else {
          newg[s].push_back(Edge(s, e.dst, e.weight, e.id));
          ne_size++;
        }
      }
    }
    auto p = chu_liu(newg, start, e_size);
    Graph compress_tree(g.size());
    Graph ans_tree(g.size());
    for (auto es : compress_tree) {
      for (auto e : es) {
        Edge prev_edge(memo[e.id]);
        ans_tree[prev_edge.src].emplace_back(prev_edge);
      }
    }
    ld fin_len = p.first + cycle_len;
    return make_pair(fin_len, ans_tree);
  }
}

int main() {
  int N, M;
  cin >> N >> M;
  vector<vector<ld>> vecs(M, vector<ld>(N));
  vector<vector<ld>> edges(M, vector<ld>(M));
  for (int i = 0; i < M; ++i) {
    for (int j = 0; j < N; ++j) {
      cin >> vecs[i][j];
    }
  }
  const int start = 0;
  const int node = 1;
  Graph g(M + 1);
  int id = 0;
  for (int i = 0; i < M; ++i) {
    ld inidis = 0;
    for (int j = 0; j < N; ++j) {
      inidis += vecs[i][j] * vecs[i][j];
    }
    g[start].emplace_back(start, node + i, inidis, id++);
    for (int j = 0; j < M; ++j) {
      if (i != j) {
        ld dis = getdis(vecs[i], vecs[j]);
        g[node + i].emplace_back(node + i, node + j, dis, id++);
      }
    }
  }
  auto p = chu_liu(g, start, (g.size()) * ((g.size() + 1)));
  cout << fixed << setprecision(22) << p.first << 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" > "D:\D_Download\Visual
///Studio 2015\Projects\programing_contest_c++\Debug\b.answer"

typedef double Weight;

struct Edge {
  int src, dst;
  Weight weight;
  int id;
  Edge(int src_, int dst_, Weight weight_, const int id_)
      : src(src_), dst(dst_), weight(weight_), id(id_) {}
  Edge(int src, int dst, Weight weight) : src(src), dst(dst), weight(weight) {}
  Edge() : src(0), dst(0), weight(0) {}
};
const Weight INF = 1e18;
const Weight ZERO = 0;
bool operator<(const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
             e.src != f.src ? e.src < f.src
                            : e.dst < f.dst;
}
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
ld getdis(const vector<ld> &f, const vector<ld> &t) {
  ld amin = -1e9;
  ld amax = 1e9;
  int n = 100;
  while (n--) {
    ld amid0 = (amin * 2 + amax) / 3;
    ld amid1 = (amin + amax * 2) / 3;
    ld len0 = 0;
    ld len1 = 0;
    {

      for (int i = 0; i < f.size(); ++i) {
        len0 += (t[i] - amid0 * f[i]) * (t[i] - amid0 * f[i]);
      }
      for (int i = 0; i < f.size(); ++i) {
        len1 += (t[i] - amid1 * f[i]) * (t[i] - amid1 * f[i]);
      }
    }
    if (len0 < len1) {
      amax = amid1;
    } else {
      amin = amid0;
    }
    if (!n)
      return len0;
  }
}
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;

namespace getcycle {
pair<int, vector<Edge>> dfs(const Graph &g, vector<int> &used, const int now,
                            const int id) {
  if (used[now] == -1) {
    used[now] = id;
    for (auto e : g[now]) {
      if (used[e.dst] == id) {
        return make_pair(e.dst, vector<Edge>(1, e));
      } else if (used[e.dst] != -1) {
        continue;
      } else {
        assert(used[e.dst] == -1);
        auto p(dfs(g, used, e.dst, id));
        if (p.first == -1) {
          return p;
        } else if (p.first == -2) {
          continue;
        } else {
          p.second.push_back(e);
          if (p.first == now) {
            return make_pair(-1, p.second);
          } else {
            return p;
          }
        }
      }
    }
    return make_pair(-2, vector<Edge>(0));
  } else {
    assert(false);
    return make_pair(0, vector<Edge>(0));
  }
}
vector<Edge> get_cycle(const Graph &g, const int start) {
  vector<int> used(g.size(), -1);

  int id = 0;
  for (int i = 0; i < g.size(); ++i) {
    if (used[i] == -1) {

      vector<Edge> cycles = dfs(g, used, i, id).second;
      id++;
      if (!cycles.empty()) {

        reverse(cycles.begin(), cycles.end());
        return cycles;
      }
    }
  }
  return vector<Edge>(0);
}
} // namespace getcycle

// aoj2309???varify??????????????£??????????????§????????????????????????
pair<Weight, Graph> chu_liu(const Graph &g, const int start, const int e_size) {
  Graph revg(g.size());

  /*????´???°???Edge?????°????????§??????*/
  vector<Edge> memo(e_size);

  for (auto es : g) {
    for (auto e : es) {
      // memo[e.id] = e;
      revg[e.dst].emplace_back(e.dst, e.src, e.weight);
    }
  }
  Graph tree(g.size());
  ld total_len = 0;
  for (int node = 0; node < g.size(); ++node) {
    if (node == start)
      continue;
    else {
      Weight amin = INF;
      Edge min_edge;
      for (auto reve : revg[node]) {
        if (amin > reve.weight) {
          amin = reve.weight;
          min_edge = Edge(reve.dst, reve.src, reve.weight);
        }
      }
      if (amin < INF) {
        total_len += min_edge.weight;
        tree[min_edge.src].emplace_back(min_edge);
      }
    }
  }
  revg.clear();
  Weight cycle_len = 0;
  vector<Edge> cycle_edges(getcycle::get_cycle(tree, start));
  for (auto e : cycle_edges) {
    cycle_len += e.weight;
  }
  if (cycle_edges.empty()) {
    return make_pair(total_len, g);
  } else {
    vector<bool> node_is_cycle(g.size());

    /*????´???°???Edge?????°????????§??????*/
    vector<int> edge_is_cycle(g.size() * g.size());

    vector<pair<int, Weight>> prevs(g.size(), make_pair(-1, ZERO));

    for (auto ce : cycle_edges) {
      node_is_cycle[ce.src] = true;
      node_is_cycle[ce.dst] = true;
      prevs[ce.dst] = make_pair(ce.src, ce.weight);
    }
    Graph newg(g.size());
    const int compress = cycle_edges[0].src;
    int ne_size = 0;
    for (int s = 0; s < g.size(); ++s) {
      bool src_is_cycle = node_is_cycle[s];
      for (auto e : g[s]) {
        bool dst_is_cycle = node_is_cycle[e.dst];
        if (src_is_cycle && dst_is_cycle) {
        } else if (src_is_cycle) {
          newg[compress].push_back(Edge(compress, e.dst, e.weight, e.id));
          ne_size++;
        } else if (dst_is_cycle) {
          newg[s].push_back(
              Edge(s, compress, e.weight - prevs[e.dst].second, e.id));
          ne_size++;
        } else {
          newg[s].push_back(Edge(s, e.dst, e.weight, e.id));
          ne_size++;
        }
      }
    }
    auto p = chu_liu(newg, start, e_size);
    Graph compress_tree(g.size());
    Graph ans_tree(g.size());
    for (auto es : compress_tree) {
      for (auto e : es) {
        Edge prev_edge(memo[e.id]);
        ans_tree[prev_edge.src].emplace_back(prev_edge);
      }
    }
    ld fin_len = p.first + cycle_len;
    return make_pair(fin_len, ans_tree);
  }
}

int main() {
  int N, M;
  cin >> N >> M;
  vector<vector<ld>> vecs(M, vector<ld>(N));
  vector<vector<ld>> edges(M, vector<ld>(M));
  for (int i = 0; i < M; ++i) {
    for (int j = 0; j < N; ++j) {
      cin >> vecs[i][j];
    }
  }
  const int start = 0;
  const int node = 1;
  Graph g(M + 1);
  int id = 0;
  for (int i = 0; i < M; ++i) {
    ld inidis = 0;
    for (int j = 0; j < N; ++j) {
      inidis += vecs[i][j] * vecs[i][j];
    }
    g[start].emplace_back(start, node + i, inidis, id++);
    for (int j = 0; j < M; ++j) {
      if (i != j) {
        ld dis = getdis(vecs[i], vecs[j]);
        g[node + i].emplace_back(node + i, node + j, dis, id++);
      }
    }
  }
  auto p = chu_liu(g, start, (g.size()) * ((g.size() + 1)));
  cout << fixed << setprecision(22) << p.first << endl;
  return 0;
}