Problem p03231 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <array>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstdio>
#include <deque>
#include <float.h>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits.h>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <vector>

using namespace std;
#define int long long

#define I32_MAX 2147483647
#define I64_MAX 9223372036854775807LL
#define I64_MAX2 1223372036854775807LL
#define INF I64_MAX2
#define MOD 1000000007
#define MEM_SIZE 10000
#define DEBUG_OUT true
#define ALL(x) (x).begin(), (x).end()

// int DP[MEM_SIZE][MEM_SIZE] = {0};
// int GMEM[MEM_SIZE][MEM_SIZE] = {0};
template <typename T> void DEBUG(T e) {
  if (DEBUG_OUT == false)
    return;
  std::cout << e << " ";
}
template <typename T> void DEBUG(const std::vector<T> &v) {
  if (DEBUG_OUT == false)
    return;
  for (const auto &e : v) {
    std::cout << e << " ";
  }
  std::cout << std::endl;
}
template <typename T> void DEBUG(const std::vector<std::vector<T>> &vv) {
  if (DEBUG_OUT == false)
    return;
  for (const auto &v : vv) {
    DEBUG(v);
  }
}
template <class T, class... Ts> void DEBUG(T d, Ts... e) {
  if (DEBUG_OUT == false)
    return;
  DEBUG(d);
  DEBUG(e...);
}
template <class T> void corner(bool flg, T hoge) {
  if (flg) {
    cout << hoge << endl;
    exit(0);
  }
}
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);
}

int gcd(int a, int b) {
  if (a < b)
    swap(a, b);
  if (a % b == 0)
    return b;
  return gcd(a % b, b);
}

void solve(void) {
  int N, M;
  cin >> N >> M;
  string S, T;
  cin >> S >> T;
  int G = gcd(N, M);
  int LCM = N * M / G;
  int P = LCM / N;
  int Q = LCM / M;
  for (int i = 1; i <= LCM; i++) {
    char X = 0;
    char Y = 0;
    if ((i - 1) % P == 0)
      X = S[(i - 1) / P];
    if ((i - 1) % Q == 0)
      Y = T[(i - 1) / Q];
    // DEBUG(X,Y);
    if (X != 0 && Y != 0) {
      if (X != Y) {
        cout << -1 << endl;
        return;
      }
    }
  }
  cout << LCM << endl;

  return;
}

int32_t main(int32_t argc, const char *argv[]) {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  std::cout << std::fixed;
  std::cout << std::setprecision(9);
  solve();

  return 0;
}


Fixed submission:
#include <algorithm>
#include <array>
#include <bitset>
#include <cmath>
#include <complex>
#include <cstdio>
#include <deque>
#include <float.h>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits.h>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <vector>

using namespace std;
#define int long long

#define I32_MAX 2147483647
#define I64_MAX 9223372036854775807LL
#define I64_MAX2 1223372036854775807LL
#define INF I64_MAX2
#define MOD 1000000007
#define MEM_SIZE 10000
#define DEBUG_OUT true
#define ALL(x) (x).begin(), (x).end()

// int DP[MEM_SIZE][MEM_SIZE] = {0};
// int GMEM[MEM_SIZE][MEM_SIZE] = {0};
template <typename T> void DEBUG(T e) {
  if (DEBUG_OUT == false)
    return;
  std::cout << e << " ";
}
template <typename T> void DEBUG(const std::vector<T> &v) {
  if (DEBUG_OUT == false)
    return;
  for (const auto &e : v) {
    std::cout << e << " ";
  }
  std::cout << std::endl;
}
template <typename T> void DEBUG(const std::vector<std::vector<T>> &vv) {
  if (DEBUG_OUT == false)
    return;
  for (const auto &v : vv) {
    DEBUG(v);
  }
}
template <class T, class... Ts> void DEBUG(T d, Ts... e) {
  if (DEBUG_OUT == false)
    return;
  DEBUG(d);
  DEBUG(e...);
}
template <class T> void corner(bool flg, T hoge) {
  if (flg) {
    cout << hoge << endl;
    exit(0);
  }
}
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);
}

int gcd(int a, int b) {
  if (a < b)
    swap(a, b);
  if (a % b == 0)
    return b;
  return gcd(a % b, b);
}

void solve(void) {
  int N, M;
  cin >> N >> M;
  string S, T;
  cin >> S >> T;
  int G = gcd(N, M);
  int LCM = N * M / G;
  int P = LCM / N;
  int Q = LCM / M;
  if (G == 1) {
    if (S[0] == T[0])
      cout << LCM << endl;
    else {
      cout << -1 << endl;
    }

    return;
  }
  for (int i = 1; i <= LCM; i++) {
    char X = 0;
    char Y = 0;
    if ((i - 1) % P == 0)
      X = S[(i - 1) / P];
    if ((i - 1) % Q == 0)
      Y = T[(i - 1) / Q];
    // DEBUG(X,Y);
    if (X != 0 && Y != 0) {
      if (X != Y) {
        cout << -1 << endl;
        return;
      }
    }
  }
  cout << LCM << endl;

  return;
}

int32_t main(int32_t argc, const char *argv[]) {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  std::cout << std::fixed;
  std::cout << std::setprecision(9);
  solve();

  return 0;
}