Problem p02580 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdlib>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <type_traits>
#include <unordered_map>
#include <utility>
#include <vector>

/* template start */

using i64 = std::int_fast64_t;
using u64 = std::uint_fast64_t;

#define rep(i, a, b) for (i64 i = (a); (i) < (b); (i)++)
#define all(i) i.begin(), i.end()

#ifdef LOCAL
#define debug(...)                                                             \
  std::cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out() { std::cerr << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head h, Tail... t) {
  std::cerr << " " << h;
  if (sizeof...(t) > 0)
    std::cout << " :";
  debug_out(t...);
}

template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &os, std::pair<T1, T2> pa) {
  return os << pa.first << " " << pa.second;
}

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return a > b && (a = b, true);
}

template <typename Num> constexpr Num mypow(Num a, u64 b, Num id = 1) {
  if (b == 0)
    return id;
  Num x = id;
  while (b > 0) {
    if (b & 1)
      x *= a;
    a *= a;
    b >>= 1;
  }
  return x;
}

/* template end */

int main() {
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);

  i64 h, w, m;
  std::cin >> h >> w >> m;

  using P = std::pair<i64, i64>;

  std::set<P> target;

  std::map<i64, i64> row, col;

  rep(i, 0, m) {
    i64 th, tw;
    std::cin >> th >> tw;

    row[th]++;
    col[tw]++;
    target.emplace(th, tw);
  }

  i64 ans = 0;

  std::vector<i64> row_vec;
  i64 row_max = 0;

  {
    for (const auto &e : row) {
      chmax(row_max, e.second);
    }

    for (const auto &e : row) {
      if (e.second == row_max)
        row_vec.emplace_back(e.first);
    }
  }

  std::vector<i64> col_vec;
  i64 col_max = 0;

  {
    for (const auto &e : col) {
      chmax(col_max, e.second);
    }

    for (const auto &e : col) {
      if (e.second == col_max)
        col_vec.emplace_back(e.first);
    }
  }

  for (const auto &r : row_vec) {
    for (const auto &c : col_vec) {
      i64 val = row_max + col_max;
      if (target.find(P(r, c)) != target.end())
        val--;
      chmax(ans, val);
    }
  }

  std::cout << ans << "\n";

  return 0;
}

Fixed submission:
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <cmath>
#include <complex>
#include <cstdint>
#include <cstdlib>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <type_traits>
#include <unordered_map>
#include <utility>
#include <vector>

/* template start */

using i64 = std::int_fast64_t;
using u64 = std::uint_fast64_t;

#define rep(i, a, b) for (i64 i = (a); (i) < (b); (i)++)
#define all(i) i.begin(), i.end()

#ifdef LOCAL
#define debug(...)                                                             \
  std::cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out() { std::cerr << std::endl; }

template <typename Head, typename... Tail> void debug_out(Head h, Tail... t) {
  std::cerr << " " << h;
  if (sizeof...(t) > 0)
    std::cout << " :";
  debug_out(t...);
}

template <typename T1, typename T2>
std::ostream &operator<<(std::ostream &os, std::pair<T1, T2> pa) {
  return os << pa.first << " " << pa.second;
}

template <typename T>
std::ostream &operator<<(std::ostream &os, std::vector<T> vec) {
  for (std::size_t i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  return os;
}

template <typename T1, typename T2> inline bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

template <typename T1, typename T2> inline bool chmin(T1 &a, T2 b) {
  return a > b && (a = b, true);
}

template <typename Num> constexpr Num mypow(Num a, u64 b, Num id = 1) {
  if (b == 0)
    return id;
  Num x = id;
  while (b > 0) {
    if (b & 1)
      x *= a;
    a *= a;
    b >>= 1;
  }
  return x;
}

/* template end */

int main() {
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);

  i64 h, w, m;
  std::cin >> h >> w >> m;

  using P = std::pair<i64, i64>;

  std::set<P> target;

  std::map<i64, i64> row, col;

  rep(i, 0, m) {
    i64 th, tw;
    std::cin >> th >> tw;

    row[th]++;
    col[tw]++;
    target.emplace(th, tw);
  }

  i64 ans = 0;

  std::vector<i64> row_vec;
  i64 row_max = 0;

  {
    for (const auto &e : row) {
      chmax(row_max, e.second);
    }

    for (const auto &e : row) {
      if (e.second == row_max)
        row_vec.emplace_back(e.first);
    }
  }

  std::vector<i64> col_vec;
  i64 col_max = 0;

  {
    for (const auto &e : col) {
      chmax(col_max, e.second);
    }

    for (const auto &e : col) {
      if (e.second == col_max)
        col_vec.emplace_back(e.first);
    }
  }

  if (row_vec.size() * col_vec.size() > m) {
    std::cout << row_max + col_max << "\n";
    return 0;
  }

  for (const auto &r : row_vec) {
    for (const auto &c : col_vec) {
      i64 val = row_max + col_max;
      if (target.find(P(r, c)) != target.end())
        val--;
      chmax(ans, val);
    }
  }

  std::cout << ans << "\n";

  return 0;
}