Problem p03034 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <array>
#include <bitset>
#include <complex>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <chrono>
#include <random>
#include <thread>
#include <unordered_map>
#include <unordered_set>

using namespace std;

#define all(c) c.begin(), c.end()
#define repeat(i, n) for (int i = 0; i < static_cast<int>(n); i++)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define dump(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define dump(x)
#endif

template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ",";
    os << *it;
  }
  return os << "}";
}

template <typename A, typename B>
ostream &operator<<(ostream &os, const pair<A, B> &v) {
  os << "{";
  os << v.first << ", " << v.second;
  return os << "}";
}

// ---------------------------------------------------------------------------

using point = complex<double>;
using ll = int64_t;

int my_main(int argc, char **argv) {
  ios::sync_with_stdio(false);
  cin.tie(0);

  ll n;
  cin >> n;
  vector<ll> s(n);
  for (ll &i : s)
    cin >> i;

  ll ret = 0;
  for (ll c = 1; c < n - 1; c++) {
    vector<bool> used(n, false);
    ll sum = 0;

    for (ll k = 1; (n - 1) - (k * c) < c; k++) {
      ll a0 = (n - 1) - k * c;
      ll a1 = k * c;

      if (used[a0])
        break;
      used[a0] = true;

      if (used[a1])
        break;
      used[a1] = true;

      sum += s[a0] + s[a1];
      ret = max(ret, sum);
    }
  }
  cout << ret << endl;

  return 0;
}

// ----------------------------------------------------------------------------
// Test driver

#ifdef DEBUG
#define MAY_RUN_TESTCASE
#endif

#ifdef MAY_RUN_TESTCASE
#include <fstream>

#if __has_include(<unistd.h>)
// Mac, Linux
#include <unistd.h>
#elif __has_include(<io.h>)
// Windows
#include <io.h>
#else
// Other?
#error "unistd.h or io.h not found"
#endif

bool test_file_exists(const std::string &str) {
  std::ifstream fs(str);
  return fs.is_open();
}

#endif

int main(int argc, char **argv) {
#ifndef MAY_RUN_TESTCASE
  return my_main(argc, argv);
#else
  if (argc == 1) {
    return my_main(argc, argv);
  } else if (argc == 2) {

    char *stdin_file = argv[1];
    freopen(stdin_file, "r", stdin);
    return my_main(argc, argv);

  } else if (argc == 5) {

    std::string stdin_file = argv[1];
    std::string expected_file = argv[2];
    std::string stdout_file = argv[3];
    std::string stderr_file = argv[4];

    if (!test_file_exists(stdin_file)) {
      std::cerr << stdin_file << " not found" << std::endl;
      return 3;
    }

    if (!test_file_exists(expected_file)) {
      std::cerr << expected_file << " not found" << std::endl;
      return 3;
    }

    int original_stdin = dup(fileno(stdin));
    int original_stdout = dup(fileno(stdout));
    int original_stderr = dup(fileno(stderr));

    freopen(stdin_file.c_str(), "r", stdin);
    freopen(stdout_file.c_str(), "w", stdout);
    freopen(stderr_file.c_str(), "w", stderr);

    int ret = my_main(argc, argv);

    fflush(stdout);
    fflush(stderr);

    dup2(original_stderr, fileno(stderr));
    dup2(original_stdout, fileno(stdout));
    dup2(original_stdin, fileno(stdin));

    if (ret != 0) {
      std::cerr << "main returns " << ret << std::endl;
      return ret;
    }

    std::ifstream inp(stdin_file);
    std::ifstream out(stdout_file);
    std::ifstream err(stderr_file);
    std::ifstream exp(expected_file);

    // Clear is needed if the file is empty.
    std::cout << "----- input -----" << std::endl;
    std::cout << inp.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "----- output ----" << std::endl;
    std::cout << out.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "---- expected ---" << std::endl;
    std::cout << exp.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "----- stderr ----" << std::endl;
    std::cout << err.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl;

    inp.seekg(0);
    out.seekg(0);
    exp.seekg(0);
    err.seekg(0);

    std::string output_str, expected_str;
    {
      std::stringstream output_ss;
      output_ss << out.rdbuf();
      output_str = output_ss.str();

      std::stringstream expected_ss;
      expected_ss << exp.rdbuf();
      expected_str = expected_ss.str();
    }

    // Remove trailing spaces
    output_str.erase(output_str.find_last_not_of(" \n\r\t") + 1);
    expected_str.erase(expected_str.find_last_not_of(" \n\r\t") + 1);

    if (output_str == expected_str)
      return 0;
    else
      return 1;
  }
  return 1;
#endif
}


Fixed submission:
#include <algorithm>
#include <array>
#include <bitset>
#include <complex>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <cctype>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <chrono>
#include <random>
#include <thread>
#include <unordered_map>
#include <unordered_set>

using namespace std;

#define all(c) c.begin(), c.end()
#define repeat(i, n) for (int i = 0; i < static_cast<int>(n); i++)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define dump(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define dump(x)
#endif

template <typename T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin())
      os << ",";
    os << *it;
  }
  return os << "}";
}

template <typename A, typename B>
ostream &operator<<(ostream &os, const pair<A, B> &v) {
  os << "{";
  os << v.first << ", " << v.second;
  return os << "}";
}

// ---------------------------------------------------------------------------

using point = complex<double>;
using ll = int64_t;

int my_main(int argc, char **argv) {
  ios::sync_with_stdio(false);
  cin.tie(0);

  ll n;
  cin >> n;
  vector<ll> s(n);
  for (ll &i : s)
    cin >> i;

  ll ret = 0;
  for (ll c = 1; c < n - 1; c++) {
    vector<bool> used(n, false);
    ll sum = 0;

    for (ll k = 1; c < (n - 1 - k * c); k++) {

      ll a0 = (n - 1) - k * c;
      ll a1 = k * c;

      if (used[a0])
        break;
      used[a0] = true;

      if (used[a1])
        break;
      used[a1] = true;

      sum += s[a0] + s[a1];
      ret = max(ret, sum);
    }
  }
  cout << ret << endl;

  return 0;
}

// ----------------------------------------------------------------------------
// Test driver

#ifdef DEBUG
#define MAY_RUN_TESTCASE
#endif

#ifdef MAY_RUN_TESTCASE
#include <fstream>

#if __has_include(<unistd.h>)
// Mac, Linux
#include <unistd.h>
#elif __has_include(<io.h>)
// Windows
#include <io.h>
#else
// Other?
#error "unistd.h or io.h not found"
#endif

bool test_file_exists(const std::string &str) {
  std::ifstream fs(str);
  return fs.is_open();
}

#endif

int main(int argc, char **argv) {
#ifndef MAY_RUN_TESTCASE
  return my_main(argc, argv);
#else
  if (argc == 1) {
    return my_main(argc, argv);
  } else if (argc == 2) {

    char *stdin_file = argv[1];
    freopen(stdin_file, "r", stdin);
    return my_main(argc, argv);

  } else if (argc == 5) {

    std::string stdin_file = argv[1];
    std::string expected_file = argv[2];
    std::string stdout_file = argv[3];
    std::string stderr_file = argv[4];

    if (!test_file_exists(stdin_file)) {
      std::cerr << stdin_file << " not found" << std::endl;
      return 3;
    }

    if (!test_file_exists(expected_file)) {
      std::cerr << expected_file << " not found" << std::endl;
      return 3;
    }

    int original_stdin = dup(fileno(stdin));
    int original_stdout = dup(fileno(stdout));
    int original_stderr = dup(fileno(stderr));

    freopen(stdin_file.c_str(), "r", stdin);
    freopen(stdout_file.c_str(), "w", stdout);
    freopen(stderr_file.c_str(), "w", stderr);

    int ret = my_main(argc, argv);

    fflush(stdout);
    fflush(stderr);

    dup2(original_stderr, fileno(stderr));
    dup2(original_stdout, fileno(stdout));
    dup2(original_stdin, fileno(stdin));

    if (ret != 0) {
      std::cerr << "main returns " << ret << std::endl;
      return ret;
    }

    std::ifstream inp(stdin_file);
    std::ifstream out(stdout_file);
    std::ifstream err(stderr_file);
    std::ifstream exp(expected_file);

    // Clear is needed if the file is empty.
    std::cout << "----- input -----" << std::endl;
    std::cout << inp.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "----- output ----" << std::endl;
    std::cout << out.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "---- expected ---" << std::endl;
    std::cout << exp.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl << std::endl;

    std::cout << "----- stderr ----" << std::endl;
    std::cout << err.rdbuf() << std::endl;
    std::cout.clear();
    std::cout << "-----------------" << std::endl;

    inp.seekg(0);
    out.seekg(0);
    exp.seekg(0);
    err.seekg(0);

    std::string output_str, expected_str;
    {
      std::stringstream output_ss;
      output_ss << out.rdbuf();
      output_str = output_ss.str();

      std::stringstream expected_ss;
      expected_ss << exp.rdbuf();
      expected_str = expected_ss.str();
    }

    // Remove trailing spaces
    output_str.erase(output_str.find_last_not_of(" \n\r\t") + 1);
    expected_str.erase(expected_str.find_last_not_of(" \n\r\t") + 1);

    if (output_str == expected_str)
      return 0;
    else
      return 1;
  }
  return 1;
#endif
}