Problem p02787 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("O3")
#define REP(i, n) for (int i = 0; i < n; i++)
#define REPP(i, n) for (int i = 1; i <= n; i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define EPS (1e-9)
#define INF (1e17)
#define PI (acos(-1))
// const double PI = acos(-1);
// const double EPS = 1e-15;
// long long INF=(long long)1E17;
#define i_7 (long long)(1e9 + 7)
// #define i_7 998'244'353
long mod(long a) {
  long long c = a % i_7;
  if (c >= 0)
    return c;
  return c + i_7;
}
long long po(long a, long b) {
  if (b == 0) {
    return 1;
  }

  long long z = po(a, b / 2);
  z = mod(z * z);
  if (b % 2 != 0) {
    z = mod(a * z);
  }
  return z;
}

bool prime_(int n) {
  if (n == 1) {
    return false;
  } else if (n == 2) {
    return true;
  } else {
    for (int i = 2; i <= std::sqrt(n); i++) {
      if (n % i == 0) {
        return false;
      }
    }
    return true;
  }
}

long long gcd_(long long a, long long b) {
  if (a < b) {
    std::swap(a, b);
  }
  if (a % b == 0) {
    return b;
  } else {
    return gcd_(b, a % b);
  }
}

long long lcm_(long long x, long long y) { return (x / gcd_(x, y)) * y; }

// using namespace std;
// using namespace boost::multiprecision;
// using namespace __gnu_pbds;

int main() {
  using namespace std;
  int h, n;
  cin >> h >> n;
  int a[n], b[n];
  REP(i, n) { cin >> a[i] >> b[i]; }
  int dp[h + 1][n];
  fill(dp[0], dp[h + 1], 1'000'000'000);
  REP(i, n) {
    REP(j, h + 1) {
      if (j == 0) {
        dp[j][i] = 0;
        continue;
      }
      if (i == 0) {
        dp[j][i] = ((j + a[i] - 1) / a[i]) * b[i];
        continue;
      }
      int q = h / a[i];
      REP(x, q + 1) {
        dp[j][i] = min(dp[j][i], dp[j - x * a[i]][i - 1] + x * b[i]);
      }
    }
  }
  int ans = dp[h][n - 1];
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
// #include <boost/multiprecision/cpp_int.hpp>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("O3")
#define REP(i, n) for (int i = 0; i < n; i++)
#define REPP(i, n) for (int i = 1; i <= n; i++)
#define ALL(obj) (obj).begin(), (obj).end()
#define EPS (1e-9)
#define INF (1e17)
#define PI (acos(-1))
// const double PI = acos(-1);
// const double EPS = 1e-15;
// long long INF=(long long)1E17;
#define i_7 (long long)(1e9 + 7)
// #define i_7 998'244'353
long mod(long a) {
  long long c = a % i_7;
  if (c >= 0)
    return c;
  return c + i_7;
}
long long po(long a, long b) {
  if (b == 0) {
    return 1;
  }

  long long z = po(a, b / 2);
  z = mod(z * z);
  if (b % 2 != 0) {
    z = mod(a * z);
  }
  return z;
}

bool prime_(int n) {
  if (n == 1) {
    return false;
  } else if (n == 2) {
    return true;
  } else {
    for (int i = 2; i <= std::sqrt(n); i++) {
      if (n % i == 0) {
        return false;
      }
    }
    return true;
  }
}

long long gcd_(long long a, long long b) {
  if (a < b) {
    std::swap(a, b);
  }
  if (a % b == 0) {
    return b;
  } else {
    return gcd_(b, a % b);
  }
}

long long lcm_(long long x, long long y) { return (x / gcd_(x, y)) * y; }

// using namespace std;
// using namespace boost::multiprecision;
// using namespace __gnu_pbds;

int main() {
  using namespace std;
  int h, n;
  cin >> h >> n;
  int a[n], b[n];
  REP(i, n) { cin >> a[i] >> b[i]; }
  int dp[h + 1][n];
  fill(dp[0], dp[h + 1], 1'000'000'000);
  REP(i, n) {
    REP(j, h + 1) {
      if (j == 0) {
        dp[j][i] = 0;
        continue;
      }
      if (i == 0) {
        dp[j][i] = ((j + a[i] - 1) / a[i]) * b[i];
        continue;
      }
      dp[j][i] = min(dp[j][i], dp[j][i - 1]);
      if (j - a[i] >= 0) {
        dp[j][i] = min(dp[j][i], dp[j - a[i]][i] + b[i]);
      } else {
        dp[j][i] = min(dp[j][i], b[i]);
      }
    }
  }
  int ans = dp[h][n - 1];
  cout << ans << endl;
  return 0;
}