Problem p02580 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin >>
#define ll long long
#define ln cout << '\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n", a)
#define mem(a) memset(a, 0, sizeof(a))
#define all(c) (c).begin(), (c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i, n) for (ll i = (ll)(n)-1; i >= 0; i--)
#define REP(i, m, n) for (ll i = (ll)(m); i < (ll)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define tr(it, c) for (iter(c) it = (c).begin(); it != (c).end(); it++)
ll check(ll n, ll m, ll x, ll y) { return x >= 0 && x < n && y >= 0 && y < m; }
void pr() { ln; }
template <class A, class... B> void pr(const A &a, const B &...b) {
  cout << a << (sizeof...(b) ? " " : "");
  pr(b...);
}
template <class A> void PR(A a, ll n) {
  rep(i, n) cout << (i ? " " : "") << a[i];
  ln;
}
const ll MAX = 1e9 + 7, MAXL = 1LL << 61, dx[8] = {-1, 0, 1, 0, -1, -1, 1, 1},
         dy[8] = {0, 1, 0, -1, -1, 1, 1, -1};
typedef pair<ll, ll> P;

class RMQ2 {
public:
  int n, dat[555555];
  void init(int _n) {
    n = 1;
    while (n < _n)
      n *= 2;
    fill(dat, dat + 2 * n - 1, -MAX);
  }
  void update(int k, int a) {
    k += n - 1;
    dat[k] = a;
    while (k > 0) {
      k = (k - 1) / 2;
      dat[k] = max(dat[k * 2 + 1], dat[k * 2 + 2]);
    }
  }
  int query(int a, int b) { return query(a, b, 0, 0, n); }
  int query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return -MAX;
    if (a <= l && r <= b)
      return dat[k];
    int vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    int vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
    return max(vl, vr);
  }
};

RMQ2 t;

void Main() {
  ll n, m, k;
  cin >> n >> m >> k;
  vector<ll> a[n], b[m];
  rep(i, k) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    a[x].pb(y);
    b[y].pb(x);
  }
  t.init(m);
  rep(i, m) t.update(i, b[i].size());
  int ans = 0;
  rep(i, n) {
    rep(j, a[i].size()) {
      ll d = t.query(a[i][j], a[i][j] + 1);
      t.update(a[i][j], d - 1);
    }
    ans = max(ans, (int)a[i].size() + t.query(0, m));
    rep(j, a[i].size()) {
      ll d = t.query(a[i][j], a[i][j] + 1);
      t.update(a[i][j], d + 1);
    }
  }
  pr(ans);
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  Main();
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin >>
#define ll long long
#define ln cout << '\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n", a)
#define mem(a) memset(a, 0, sizeof(a))
#define all(c) (c).begin(), (c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i, n) for (ll i = (ll)(n)-1; i >= 0; i--)
#define REP(i, m, n) for (ll i = (ll)(m); i < (ll)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define tr(it, c) for (iter(c) it = (c).begin(); it != (c).end(); it++)
ll check(ll n, ll m, ll x, ll y) { return x >= 0 && x < n && y >= 0 && y < m; }
void pr() { ln; }
template <class A, class... B> void pr(const A &a, const B &...b) {
  cout << a << (sizeof...(b) ? " " : "");
  pr(b...);
}
template <class A> void PR(A a, ll n) {
  rep(i, n) cout << (i ? " " : "") << a[i];
  ln;
}
const ll MAX = 1e9 + 7, MAXL = 1LL << 61, dx[8] = {-1, 0, 1, 0, -1, -1, 1, 1},
         dy[8] = {0, 1, 0, -1, -1, 1, 1, -1};
typedef pair<ll, ll> P;

class RMQ2 {
public:
  int n, dat[1555555];
  void init(int _n) {
    n = 1;
    while (n < _n)
      n *= 2;
    fill(dat, dat + 2 * n - 1, -MAX);
  }
  void update(int k, int a) {
    k += n - 1;
    dat[k] = a;
    while (k > 0) {
      k = (k - 1) / 2;
      dat[k] = max(dat[k * 2 + 1], dat[k * 2 + 2]);
    }
  }
  int query(int a, int b) { return query(a, b, 0, 0, n); }
  int query(int a, int b, int k, int l, int r) {
    if (r <= a || b <= l)
      return -MAX;
    if (a <= l && r <= b)
      return dat[k];
    int vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    int vr = query(a, b, k * 2 + 2, (l + r) / 2, r);
    return max(vl, vr);
  }
};

RMQ2 t;

void Main() {
  ll n, m, k;
  cin >> n >> m >> k;
  vector<ll> a[n], b[m];
  rep(i, k) {
    int x, y;
    cin >> x >> y;
    x--, y--;
    a[x].pb(y);
    b[y].pb(x);
  }
  t.init(m);
  rep(i, m) t.update(i, b[i].size());
  int ans = 0;
  rep(i, n) {
    rep(j, a[i].size()) {
      ll d = t.query(a[i][j], a[i][j] + 1);
      t.update(a[i][j], d - 1);
    }
    ans = max(ans, (int)a[i].size() + t.query(0, m));
    rep(j, a[i].size()) {
      ll d = t.query(a[i][j], a[i][j] + 1);
      t.update(a[i][j], d + 1);
    }
  }
  pr(ans);
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  Main();
  return 0;
}