Problem p03630 (C++)

Buggy submission (status: Time Limit Exceeded):
#line 2 "/Users/kaage/Desktop/ProgrammingWorkspace/library/other/template.hpp"
#define _CRT_SECURE_NO_WARNINGS
#pragma target("avx2")
#pragma optimize("O3")
#pragma optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define REP(i, n) for (int i = 1; i <= (n); i++)
#define all(V) V.begin(), V.end()
typedef unsigned int uint;
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<int, int> P;
typedef std::pair<lint, lint> LP;
constexpr int INF = INT_MAX / 2;
constexpr lint LINF = LLONG_MAX / 2;
constexpr double eps = DBL_EPSILON;
constexpr double PI = 3.141592653589793238462643383279;
template <class T>
class prique : public std::priority_queue<T, std::vector<T>, std::greater<T>> {
};
template <class T, class U> inline bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <class T, class U> inline bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
inline lint gcd(lint a, lint b) {
  while (b) {
    lint c = a;
    a = b;
    b = c % b;
  }
  return a;
}
inline lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }
bool isprime(lint n) {
  if (n == 1)
    return false;
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0)
      return false;
  }
  return true;
}
template <typename T> T mypow(T a, lint b) {
  T res(1);
  while (b) {
    if (b & 1)
      res *= a;
    a *= a;
    b >>= 1;
  }
  return res;
}
lint modpow(lint a, lint b, lint m) {
  lint res(1);
  while (b) {
    if (b & 1) {
      res *= a;
      res %= m;
    }
    a *= a;
    a %= m;
    b >>= 1;
  }
  return res;
}
template <typename T> void printArray(std::vector<T> &vec) {
  rep(i, vec.size()) {
    std::cout << vec[i];
    std::cout << (i == (int)vec.size() - 1 ? "\n" : " ");
  }
}
template <typename T> void printArray(T l, T r) {
  T rprev = std::prev(r);
  for (T i = l; i != rprev; i++) {
    std::cout << *i << " ";
  }
  std::cout << *rprev << std::endl;
}
LP extGcd(lint a, lint b) {
  if (b == 0)
    return {1, 0};
  LP s = extGcd(b, a % b);
  std::swap(s.first, s.second);
  s.second -= a / b * s.first;
  return s;
}
LP ChineseRem(const lint &b1, const lint &m1, const lint &b2, const lint &m2) {
  lint p = extGcd(m1, m2).first;
  lint tmp = (b2 - b1) * p % m2;
  lint r = (b1 + m1 * tmp + m1 * m2) % (m1 * m2);
  return std::make_pair(r, m1 * m2);
}
template <typename F> inline constexpr decltype(auto) lambda_fix(F &&f) {
  return [f = std::forward<F>(f)](auto &&...args) {
    return f(f, std::forward<decltype(args)>(args)...);
  };
}
#line 3 "/Users/kaage/Desktop/ProgrammingWorkspace/library/data-structure/SparseTable.hpp"
template <typename T> class SparseTable {
  std::vector<std::vector<T>> table;
  std::vector<int> logtable;

public:
  SparseTable(std::vector<T> vec) {
    int maxlength = 0;
    while ((1 << (maxlength + 1)) <= vec.size())
      maxlength++;
    table.resize(maxlength + 1, std::vector<T>(vec.size()));
    logtable.resize(vec.size() + 1);
    rep(i, maxlength + 1) {
      rep(j, vec.size() - (1 << i) + 1) {
        if (i) {
          table[i][j] =
              std::min(table[i - 1][j], table[i - 1][j + (1 << (i - 1))]);
        } else
          table[i][j] = vec[j];
      }
    }
    logtable[1] = 0;
    for (int i = 2; i <= vec.size(); i++) {
      logtable[i] = logtable[i >> 1] + 1;
    }
  }
  template <class InputIter> SparseTable(InputIter first, InputIter last) {
    std::vector<T> vec;
    while (first != last) {
      vec.emplace_back(*first);
    }
  }
  T query(int l, int r) {
    int length = r - l;
    return std::min(table[logtable[length]][l],
                    table[logtable[length]][r - (1 << logtable[length])]);
  }
};
#line 3 "main.cpp"
int H, W;
char s[2010][2010];
std::vector<int> c[2010];
int main() {
  std::cin >> H >> W;
  rep(i, H) { rep(j, W) std::cin >> s[i][j]; }
  rep(i, H - 1) {
    rep(j, W - 1) {
      if ((s[i][j] == s[i][j + 1]) != (s[i + 1][j] == s[i + 1][j + 1]))
        c[i].emplace_back(j);
    }
  }
  int ans = std::max(H, W);
  rep(i, W - 1) {
    std::vector<P> vec;
    rep(j, H - 1) {
      auto ite = std::lower_bound(all(c[j]), i);
      int x = ite != c[j].end() ? *ite : W - 1;
      vec.emplace_back(x, j);
    }
    std::set<P> interval;
    std::set<int> len;
    interval.insert({0, H});
    len.insert(H);
    std::sort(all(vec));
    int now = 0;
    for (int j = i; j < W; j++) {
      chmax(ans, (j - i + 1) * (*len.rbegin()));
      while (now < vec.size() && vec[now].first <= j) {
        auto ite = --interval.upper_bound({vec[now].second, INF});
        len.erase(ite->second - ite->first);
        interval.insert({ite->first, vec[now].second + 1});
        len.insert(vec[now].second + 1 - ite->first);
        interval.insert({vec[now].second + 1, ite->second});
        len.insert(ite->second - vec[now].second - 1);
        interval.erase(ite);
        now++;
      }
    }
  }
  std::cout << ans << std::endl;
  return 0;
}

Fixed submission:
#line 2 "/Users/kaage/Desktop/ProgrammingWorkspace/library/other/template.hpp"
#define _CRT_SECURE_NO_WARNINGS
#pragma target("avx2")
#pragma optimize("O3")
#pragma optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string.h>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define REP(i, n) for (int i = 1; i <= (n); i++)
#define all(V) V.begin(), V.end()
typedef unsigned int uint;
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<int, int> P;
typedef std::pair<lint, lint> LP;
constexpr int INF = INT_MAX / 2;
constexpr lint LINF = LLONG_MAX / 2;
constexpr double eps = DBL_EPSILON;
constexpr double PI = 3.141592653589793238462643383279;
template <class T>
class prique : public std::priority_queue<T, std::vector<T>, std::greater<T>> {
};
template <class T, class U> inline bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
template <class T, class U> inline bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) {
    lhs = rhs;
    return 1;
  }
  return 0;
}
inline lint gcd(lint a, lint b) {
  while (b) {
    lint c = a;
    a = b;
    b = c % b;
  }
  return a;
}
inline lint lcm(lint a, lint b) { return a / gcd(a, b) * b; }
bool isprime(lint n) {
  if (n == 1)
    return false;
  for (int i = 2; i * i <= n; i++) {
    if (n % i == 0)
      return false;
  }
  return true;
}
template <typename T> T mypow(T a, lint b) {
  T res(1);
  while (b) {
    if (b & 1)
      res *= a;
    a *= a;
    b >>= 1;
  }
  return res;
}
lint modpow(lint a, lint b, lint m) {
  lint res(1);
  while (b) {
    if (b & 1) {
      res *= a;
      res %= m;
    }
    a *= a;
    a %= m;
    b >>= 1;
  }
  return res;
}
template <typename T> void printArray(std::vector<T> &vec) {
  rep(i, vec.size()) {
    std::cout << vec[i];
    std::cout << (i == (int)vec.size() - 1 ? "\n" : " ");
  }
}
template <typename T> void printArray(T l, T r) {
  T rprev = std::prev(r);
  for (T i = l; i != rprev; i++) {
    std::cout << *i << " ";
  }
  std::cout << *rprev << std::endl;
}
LP extGcd(lint a, lint b) {
  if (b == 0)
    return {1, 0};
  LP s = extGcd(b, a % b);
  std::swap(s.first, s.second);
  s.second -= a / b * s.first;
  return s;
}
LP ChineseRem(const lint &b1, const lint &m1, const lint &b2, const lint &m2) {
  lint p = extGcd(m1, m2).first;
  lint tmp = (b2 - b1) * p % m2;
  lint r = (b1 + m1 * tmp + m1 * m2) % (m1 * m2);
  return std::make_pair(r, m1 * m2);
}
template <typename F> inline constexpr decltype(auto) lambda_fix(F &&f) {
  return [f = std::forward<F>(f)](auto &&...args) {
    return f(f, std::forward<decltype(args)>(args)...);
  };
}
#line 3 "/Users/kaage/Desktop/ProgrammingWorkspace/library/data-structure/SparseTable.hpp"
template <typename T> class SparseTable {
  std::vector<std::vector<T>> table;
  std::vector<int> logtable;

public:
  SparseTable(std::vector<T> vec) {
    int maxlength = 0;
    while ((1 << (maxlength + 1)) <= vec.size())
      maxlength++;
    table.resize(maxlength + 1, std::vector<T>(vec.size()));
    logtable.resize(vec.size() + 1);
    rep(i, maxlength + 1) {
      rep(j, vec.size() - (1 << i) + 1) {
        if (i) {
          table[i][j] =
              std::min(table[i - 1][j], table[i - 1][j + (1 << (i - 1))]);
        } else
          table[i][j] = vec[j];
      }
    }
    logtable[1] = 0;
    for (int i = 2; i <= vec.size(); i++) {
      logtable[i] = logtable[i >> 1] + 1;
    }
  }
  template <class InputIter> SparseTable(InputIter first, InputIter last) {
    std::vector<T> vec;
    while (first != last) {
      vec.emplace_back(*first);
    }
  }
  T query(int l, int r) {
    int length = r - l;
    return std::min(table[logtable[length]][l],
                    table[logtable[length]][r - (1 << logtable[length])]);
  }
};
#line 3 "main.cpp"
int H, W;
char s[2010][2010];
std::vector<int> c[2010];
int main() {
  std::cin >> H >> W;
  rep(i, H) { rep(j, W) std::cin >> s[i][j]; }
  rep(i, H - 1) {
    rep(j, W - 1) {
      if ((s[i][j] == s[i][j + 1]) != (s[i + 1][j] == s[i + 1][j + 1]))
        c[i].emplace_back(j);
    }
  }
  int ans = std::max(H, W);
  rep(i, W - 1) {
    std::vector<P> vec;
    rep(j, H - 1) {
      auto ite = std::lower_bound(all(c[j]), i);
      int x = ite != c[j].end() ? *ite : W - 1;
      vec.emplace_back(x, j);
    }
    std::set<P> interval;
    std::set<int> len;
    interval.insert({0, H});
    len.insert(H);
    std::sort(all(vec));
    int now = 0;
    for (int j = i; j < W; j++) {
      if ((W - i + 1) * (*len.rbegin()) <= ans)
        break;
      chmax(ans, (j - i + 1) * (*len.rbegin()));
      while (now < vec.size() && vec[now].first <= j) {
        auto ite = --interval.upper_bound({vec[now].second, INF});
        len.erase(ite->second - ite->first);
        interval.insert({ite->first, vec[now].second + 1});
        len.insert(vec[now].second + 1 - ite->first);
        interval.insert({vec[now].second + 1, ite->second});
        len.insert(ite->second - vec[now].second - 1);
        interval.erase(ite);
        now++;
      }
    }
  }
  std::cout << ans << std::endl;
  return 0;
}