Problem p01827 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

struct UnionFind {
  vector<int> data;
  UnionFind(int size) : data(size, -1) {}
  UnionFind() {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

vector<set<int>> G;
UnionFind uf;
vi lv;

void add_edge(int _a, int _b) {
  int a = uf.root(_a), b = uf.root(_b);
  if (a == b)
    return;

  if (lv[a] > lv[b])
    swap(a, b);
  if (lv[a] != lv[b]) {
    G[a].insert(b);
    return;
  }

  // lv[a] == lv[b]
  uf.unionSet(a, b);
  if (uf.root(a) != a)
    swap(a, b);
  assert(uf.root(a) == a);
  for (auto &e : G[b]) {
    G[a].insert(e);
  }
  G[b].clear();
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  lv = vi(n);
  for (auto &e : lv)
    cin >> e;
  uf = UnionFind(n);
  G = vector<set<int>>(n);
  int m;
  cin >> m;

  using Elem = tuple<int, int>;
  vector<vector<Elem>> org(n);
  rep(i, m) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    add_edge(a, b);

    org[a].emplace_back(Elem(lv[b], b));
    org[b].emplace_back(Elem(lv[a], a));
  }

  rep(i, n) {
    sort(_all(org[i]));
    int len = org[i].size();
    rep(j, len - 1) {
      int a;
      tie(ignore, a) = org[i][j];
      int b;
      tie(ignore, b) = org[i][j + 1];
      add_edge(a, b);
    }
  }

  priority_queue<Elem, vector<Elem>, greater<Elem>> q;
  rep(i, n) q.push(Elem(lv[i], i));
  vi cost(n);
  ll res = 0;
  while (q.size()) {
    Elem cur = q.top();
    q.pop();
    int _v;
    tie(ignore, _v) = cur;
    int v = uf.root(_v);
    if (v != _v)
      continue;

    if (cost[v] == 0)
      cost[v] = 1;
    res += cost[v];

    for (int _nv : G[v]) {
      int nv = uf.root(_nv);
      chmax(cost[nv], cost[v] + 1);
    }
  }
  rep(_v, n) {
    int v = uf.root(_v);
    if (v == _v)
      continue;
    res += cost[v];
  }

  cout << res << endl;

  return 0;
}

Error: 0
0: 1
1: 2
2: 2


Fixed submission:

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  vi lv(n);
  for (auto &e : lv)
    cin >> e;

  int m;
  cin >> m;
  vector<vi> G(n);
  rep(loop, m) {
    int a, b;
    cin >> a >> b;
    a--, b--;
    G[a].emplace_back(b);
    G[b].emplace_back(a);
  }

  using Elem = tuple<int, int>;
  priority_queue<Elem, vector<Elem>, greater<Elem>> q;
  rep(i, n) { q.push(Elem(lv[i], i)); }

  vi high(n, -1);
  vi cost(n, -1);
  while (q.size()) {
    Elem cur = q.top();
    q.pop();
    int v;
    tie(ignore, v) = cur;

    cost[v] = 1;
    auto update = [&](int vv) {
      if (vv == -1)
        return;
      if (lv[vv] < lv[v] and cost[vv] >= cost[v]) {
        chmax(cost[v], cost[vv] + 1);
      } else if (lv[vv] == lv[v]) {
        chmax(cost[v], cost[vv]);
      }
    };
    for (auto &nv : G[v]) {
      // cerr << "v = " << v << ", nv = " << nv << ", high[nv] = " << high[nv]
      // << endl;
      update(nv);
      update(high[nv]);
    }
    for (auto &nv : G[v]) {
      int u = high[nv];
      if (u == -1)
        high[nv] = v;
      else if (cost[u] <= cost[v]) {
        high[nv] = v;
      }
    }
    cerr << v << ": " << cost[v] << endl;
  }

  int res = 0;
  for (auto &e : cost)
    res += e;
  cout << res << endl;

  return 0;
}