Problem p02580 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;
using ll = long long;

#define fast                                                                   \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);                                                                  \
  cout.tie(0)

#define endl "\n"
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define int long long int
#define pll pair<int, int>

#define ALL(v) v.begin(), v.end()
#define ALLR(v) v.rbegin(), v.rend()
#define pii 3.14159265358979323
#define inf LLONG_MAX
#define ones(x) __builtin_popcount(x)
#define fill(a, b) memset(a, b, sizeof(a))
#define mod 1000000007
#define hell 998244353

ll mod_pow(ll a, ll b, ll m) {
  ll res = 1;
  while (b) {
    if (b & 1) {
      res = (res * a) % m;
    }
    a = (a * a) % m;
    b >>= 1;
  }
  return res;
}

ll mod_inverse(ll a) { return mod_pow(a, mod - 2, mod); }

struct CustomCompare {
  bool operator()(const pair<int, int> &l, const pair<int, int> &r) {
    return l.S < r.S;
  }
};

void solve() {
  int n, m, p;

  cin >> n >> m >> p;

  vector<pair<int, int>> a(p);

  for (int i = 0; i < p; ++i) {
    cin >> a[i].F >> a[i].S;
  }

  sort(ALL(a));

  map<int, int> f;

  multiset<int> mt;

  for (int i = 0; i < p; ++i) {
    f[a[i].S]++;
  }

  for (auto u : f) {
    mt.insert(u.S);
  }

  int mx = 0;

  for (int i = 0; i < p; ++i) {
    int j = i;

    while (j < p && a[i].F == a[j].F) {
      mt.erase(mt.find(f[a[i].S]));
      mt.insert(f[a[i].S] - 1);
      j++;
    }

    auto tm = mt.end();
    tm--;

    mx = max(mx, j - i + (*tm));

    for (int z = i; z < j; ++z) {
      mt.erase(mt.find(f[a[z].S] - 1));
      mt.insert(f[a[z].S]);
    }

    i = j - 1;
  }

  cout << mx;
}

signed main() {
  fast;

  int t = 1;

  // cin >> t;

  while (t--) {
    solve();
  }

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;
using ll = long long;

#define fast                                                                   \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);                                                                  \
  cout.tie(0)

#define endl "\n"
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define int long long int
#define pll pair<int, int>

#define ALL(v) v.begin(), v.end()
#define ALLR(v) v.rbegin(), v.rend()
#define pii 3.14159265358979323
#define inf LLONG_MAX
#define ones(x) __builtin_popcount(x)
#define fill(a, b) memset(a, b, sizeof(a))
#define mod 1000000007
#define hell 998244353

ll mod_pow(ll a, ll b, ll m) {
  ll res = 1;
  while (b) {
    if (b & 1) {
      res = (res * a) % m;
    }
    a = (a * a) % m;
    b >>= 1;
  }
  return res;
}

ll mod_inverse(ll a) { return mod_pow(a, mod - 2, mod); }

struct CustomCompare {
  bool operator()(const pair<int, int> &l, const pair<int, int> &r) {
    return l.S < r.S;
  }
};

void solve() {
  int n, m, p;

  cin >> n >> m >> p;

  vector<pair<int, int>> a(p);

  for (int i = 0; i < p; ++i) {
    cin >> a[i].F >> a[i].S;
  }

  sort(ALL(a));

  map<int, int> f;

  multiset<int> mt;

  for (int i = 0; i < p; ++i) {
    f[a[i].S]++;
  }

  for (auto u : f) {
    mt.insert(u.S);
  }

  int mx = 0;

  for (int i = 0; i < p; ++i) {
    int j = i;

    while (j < p && a[i].F == a[j].F) {
      mt.erase(mt.find(f[a[j].S]));
      mt.insert(f[a[j].S] - 1);
      j++;
    }

    auto tm = mt.end();
    tm--;

    mx = max(mx, j - i + (*tm));

    for (int z = i; z < j; ++z) {
      mt.erase(mt.find(f[a[z].S] - 1));
      mt.insert(f[a[z].S]);
    }

    i = j - 1;
  }

  cout << mx;
}

signed main() {
  fast;

  int t = 1;

  // cin >> t;

  while (t--) {
    solve();
  }

  return 0;
}