Problem p02695 (C++)

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

using namespace std;

vector<string> split(const string &s, char delim) {
  vector<string> elems;
  string item;
  for (char ch : s) {
    if (ch == delim) {
      if (!item.empty()) {
        elems.push_back(item);
      }
      item.clear();
    } else {
      item += ch;
    }
  }
  if (!item.empty()) {
    elems.push_back(item);
  }
  return elems;
}

string to_str_with_zero(int i, int w) {
  ostringstream sout;
  sout << std::setfill('0') << std::setw(w) << i;
  string s = sout.str();
  return s;
}

int letter_to_int(char c) { return tolower(c) - 'a'; }

int compare_array(vector<int> a1, vector<int> a2) {
  if (a1.size() != a2.size()) {
    return a1.size() - a2.size();
  }
  for (int i = 0; i < a1.size(); i++) {
    if (a1.at(i) != a2.at(i)) {
      return a1.at(i) - a2.at(i);
    }
  }
  return 0;
}

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

char int_to_char(int a) {
  if (a == -1) {
    return 'z';
  } else {
    return 'a' + a;
  }
}

long nCr(int n, int r) {
  long ans = 1;
  for (int i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (int i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}

long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

int divide_count(int a, int divider) {
  int r = 0;
  while (a % divider == 0) {
    a /= divider;
    r++;
  }
  return r;
}

bool is_prime(int a) {
  int i = 2;
  while (i * i <= a) {
    if (a % i == 0) {
      return false;
    }
    i++;
  }
  return true;
}

vector<vector<int>> all_comb(int n, int k) {
  vector<vector<int>> combs(nCr(n, k), vector<int>(k));
  for (int i = 0; i < k; i++) {
    combs[0][i] = i;
    combs[1][i] = i;
  }

  for (long i = 1; i < nCr(n, k); i++) {
    int p = 1;
    while (combs[i][k - p] == n - p) {
      p++;
      if (p > k) {
        break;
      }
    }
    combs[i][k - p]++;
    int q = combs[i][k - p];
    for (int j = 1; j < p; j++) {
      combs[i][k - p + j] = q + j;
    }

    if (i < nCr(n, k) - 1) {
      for (int j = 0; j < k; j++) {
        combs[i + 1][j] = combs[i][j];
      }
    }
  }

  return combs;
}

int main() {
  std::cout << std::setprecision(9);
  int n, m, q;
  cin >> n >> m >> q;

  vector<vector<int>> c(q, vector<int>(4));
  for (int i = 0; i < q; i++) {
    cin >> c[i][0] >> c[i][1] >> c[i][2] >> c[i][3];
  }

  vector<vector<int>> combs = all_comb(m, n);

  int max = 0;
  vector<int> comb(n);
  for (int i = 0; i < n; i++) {
    comb[i] = 0;
  }
  while (true) {
    int score = 0;
    for (int i = 0; i < q; i++) {
      if (comb[c[i][1] - 1] - comb[c[i][0] - 1] == c[i][2]) {
        score += c[i][3];
      }
    }
    if (score > max) {
      max = score;
    }

    int p = n - 1;
    while (comb[p] == m - 1) {
      p--;
      if (p < 0) {
        break;
      }
    }
    if (p < 0) {
      break;
    }
    comb[p]++;
    for (int i = p + 1; i < n; i++) {
      comb[i] = comb[p];
    }
  }

  cout << max << endl;
}

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

using namespace std;

vector<string> split(const string &s, char delim) {
  vector<string> elems;
  string item;
  for (char ch : s) {
    if (ch == delim) {
      if (!item.empty()) {
        elems.push_back(item);
      }
      item.clear();
    } else {
      item += ch;
    }
  }
  if (!item.empty()) {
    elems.push_back(item);
  }
  return elems;
}

string to_str_with_zero(int i, int w) {
  ostringstream sout;
  sout << std::setfill('0') << std::setw(w) << i;
  string s = sout.str();
  return s;
}

int letter_to_int(char c) { return tolower(c) - 'a'; }

int compare_array(vector<int> a1, vector<int> a2) {
  if (a1.size() != a2.size()) {
    return a1.size() - a2.size();
  }
  for (int i = 0; i < a1.size(); i++) {
    if (a1.at(i) != a2.at(i)) {
      return a1.at(i) - a2.at(i);
    }
  }
  return 0;
}

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

char int_to_char(int a) {
  if (a == -1) {
    return 'z';
  } else {
    return 'a' + a;
  }
}

long nCr(int n, int r) {
  long ans = 1;
  for (int i = n; i > n - r; --i) {
    ans = ans * i;
  }
  for (int i = 1; i < r + 1; ++i) {
    ans = ans / i;
  }
  return ans;
}

long long modinv(long long a, long long m) {
  long long b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}

int divide_count(int a, int divider) {
  int r = 0;
  while (a % divider == 0) {
    a /= divider;
    r++;
  }
  return r;
}

bool is_prime(int a) {
  int i = 2;
  while (i * i <= a) {
    if (a % i == 0) {
      return false;
    }
    i++;
  }
  return true;
}

vector<vector<int>> all_comb(int n, int k) {
  vector<vector<int>> combs(nCr(n, k), vector<int>(k));
  for (int i = 0; i < k; i++) {
    combs[0][i] = i;
    combs[1][i] = i;
  }

  for (long i = 1; i < nCr(n, k); i++) {
    int p = 1;
    while (combs[i][k - p] == n - p) {
      p++;
      if (p > k) {
        break;
      }
    }
    combs[i][k - p]++;
    int q = combs[i][k - p];
    for (int j = 1; j < p; j++) {
      combs[i][k - p + j] = q + j;
    }

    if (i < nCr(n, k) - 1) {
      for (int j = 0; j < k; j++) {
        combs[i + 1][j] = combs[i][j];
      }
    }
  }

  return combs;
}

int main() {
  std::cout << std::setprecision(9);
  int n, m, q;
  cin >> n >> m >> q;

  vector<vector<int>> c(q, vector<int>(4));
  for (int i = 0; i < q; i++) {
    cin >> c[i][0] >> c[i][1] >> c[i][2] >> c[i][3];
  }

  int max = 0;
  vector<int> comb(n);
  for (int i = 0; i < n; i++) {
    comb[i] = 0;
  }
  while (true) {
    int score = 0;
    for (int i = 0; i < q; i++) {
      if (comb[c[i][1] - 1] - comb[c[i][0] - 1] == c[i][2]) {
        score += c[i][3];
      }
    }
    if (score > max) {
      max = score;
    }

    int p = n - 1;
    while (comb[p] == m - 1) {
      p--;
      if (p < 0) {
        break;
      }
    }
    if (p < 0) {
      break;
    }
    comb[p]++;
    for (int i = p + 1; i < n; i++) {
      comb[i] = comb[p];
    }
  }

  cout << max << endl;
}