Problem p03421 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define ALL(a) begin(a), end(a)
#define SZ(a) ((int)(a).size())
#define rep(i, n) for (int i = 0; i < n; i++)

#ifdef __DEBUG
#define debug if (true)
#else
#define debug if (false)
#endif

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

template <typename T> struct vector2 : public vector<vector<T>> {
  vector2(int n, int m, const T &k = T())
      : vector<vector<T>>(n, vector<T>(m, k)) {}
};
template <typename T> struct vector3 : public vector<vector2<T>> {
  vector3(int n, int m, int k, const T &l = T())
      : vector<vector2<T>>(n, vector2<T>(m, k, l)) {}
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n, inc, dec;
  cin >> n >> inc >> dec;
  bool rev = inc < dec;
  if (rev) {
    debug puts("REV");
    swap(inc, dec);
  }
  if (dec == 0) {
    puts("-1");
    return 0;
  }
  if (inc + dec - 1 > n) {
    puts("-1");
    return 0;
  }
  if (1LL * inc * (inc + dec - 1) < n) {
    puts("-1");
    return 0;
  }
  int rem = n - inc;
  int last = 0;
  vi ans;
  for (int iter = 0; iter < inc; iter++) {
    int take = min(dec - 1, rem);
    rem -= take;
    for (int i = last + take + 1; i > last; i--) {
      debug printf("PB %d\n", i);
      ans.push_back(i);
    }
    last = last + take + 1;
  }
  if (rev) {
    for (int &i : ans)
      i = n + 1 - i;
  }
  assert(SZ(ans) == n);
  for (int i = 0; i < SZ(ans); i++) {
    printf("%d%c", ans[i], i == SZ(ans) - 1 ? '\n' : ' ');
  }
  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define ALL(a) begin(a), end(a)
#define SZ(a) ((int)(a).size())
#define rep(i, n) for (int i = 0; i < n; i++)

#ifdef __DEBUG
#define debug if (true)
#else
#define debug if (false)
#endif

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

template <typename T> struct vector2 : public vector<vector<T>> {
  vector2(int n, int m, const T &k = T())
      : vector<vector<T>>(n, vector<T>(m, k)) {}
};
template <typename T> struct vector3 : public vector<vector2<T>> {
  vector3(int n, int m, int k, const T &l = T())
      : vector<vector2<T>>(n, vector2<T>(m, k, l)) {}
};

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int n, inc, dec;
  cin >> n >> inc >> dec;
  bool rev = inc < dec;
  if (rev) {
    debug puts("REV");
    swap(inc, dec);
  }
  if (dec == 0) {
    puts("-1");
    return 0;
  }
  if (inc + dec - 1 > n) {
    puts("-1");
    return 0;
  }
  if (1LL * inc * dec < n) {
    puts("-1");
    return 0;
  }
  int rem = n - inc;
  int last = 0;
  vi ans;
  for (int iter = 0; iter < inc; iter++) {
    int take = min(dec - 1, rem);
    rem -= take;
    for (int i = last + take + 1; i > last; i--) {
      debug printf("PB %d\n", i);
      ans.push_back(i);
    }
    last = last + take + 1;
  }
  if (rev) {
    for (int &i : ans)
      i = n + 1 - i;
  }
  assert(SZ(ans) == n);
  for (int i = 0; i < SZ(ans); i++) {
    printf("%d%c", ans[i], i == SZ(ans) - 1 ? '\n' : ' ');
  }
  return 0;
}