Problem p02665 (C++)

Buggy submission (status: Runtime Error):
// clang-format off
#include <bits/stdc++.h>

#define mp make_pair
#define fst first
#define snd second
#define forn(i,n) for (int i = 0; i < int(n); i++)
#define forn1(i,n) for (int i = 1; i <= int(n); i++)
#define popcnt __builtin_popcount
#define ffs __builtin_ffs
#define ctz __builtin_ctz
#define clz __builtin_clz
#define all(a) (a).begin(), (a).end()
 
using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pli = pair<ll,int>;
using pil = pair<int,ll>;
using pll = pair<ll,ll>;
template <typename T> using vec = vector<T>;
using vi = vec<int>;
using vl = vec<ll>;
template <typename T> using que = queue<T>;
template <typename T> using deq = deque<T>;

template <typename T> T id(T b) {return b;};
template <typename T> void chmax(T &x, T y) {if (x < y) x = y;}
template <typename T> void chmin(T &x, T y) {if (x > y) x = y;}
template <typename S, typename K> bool contains(S &s, K k) { return s.find(k) != s.end(); }
void fastio() { ios_base::sync_with_stdio(false); cin.tie(nullptr); }
constexpr ll TEN(int n) { if (n == 0) return 1LL; else return 10LL*TEN(n-1); }
// clang-format on

const int MAX_N = 100000;
int n;
ll a[MAX_N];
ll mx[MAX_N + 2];
ll mn[MAX_N + 1];

int main() {
  fastio();

  cin >> n;
  forn(i, n + 1) cin >> a[i];

  mx[n] = a[n];
  for (int i = n - 1; i >= 0; i--) {
    mx[i] = a[i] + mx[i + 1];
  }

  bool ok = true;

  ll ans = mn[0] = 1;
  ok &= mn[0] >= a[0];
  for (int i = 1; i <= n; i++) {
    mn[i] = min(2LL * (mn[i - 1] - a[i - 1]), mx[i]);
    ok &= mn[i] >= a[i];
    ans += mn[i];
  }

  ok &= mn[n] == a[n];

  if (ok) {
    cout << ans << endl;
  } else {
    cout << -1 << endl;
  }

  return 0;
}

Fixed submission:
// clang-format off
#include <bits/stdc++.h>

#define mp make_pair
#define fst first
#define snd second
#define forn(i,n) for (int i = 0; i < int(n); i++)
#define forn1(i,n) for (int i = 1; i <= int(n); i++)
#define popcnt __builtin_popcount
#define ffs __builtin_ffs
#define ctz __builtin_ctz
#define clz __builtin_clz
#define all(a) (a).begin(), (a).end()
 
using namespace std;

using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pli = pair<ll,int>;
using pil = pair<int,ll>;
using pll = pair<ll,ll>;
template <typename T> using vec = vector<T>;
using vi = vec<int>;
using vl = vec<ll>;
template <typename T> using que = queue<T>;
template <typename T> using deq = deque<T>;

template <typename T> T id(T b) {return b;};
template <typename T> void chmax(T &x, T y) {if (x < y) x = y;}
template <typename T> void chmin(T &x, T y) {if (x > y) x = y;}
template <typename S, typename K> bool contains(S &s, K k) { return s.find(k) != s.end(); }
void fastio() { ios_base::sync_with_stdio(false); cin.tie(nullptr); }
constexpr ll TEN(int n) { if (n == 0) return 1LL; else return 10LL*TEN(n-1); }
// clang-format on

const int MAX_N = 100000;
int n;
ll a[MAX_N + 1];
ll mx[MAX_N + 1];
ll mn[MAX_N + 1];

int main() {
  fastio();

  cin >> n;
  forn(i, n + 1) cin >> a[i];

  mx[n] = a[n];
  for (int i = n - 1; i >= 0; i--) {
    mx[i] = a[i] + mx[i + 1];
  }

  bool ok = true;

  ll ans = mn[0] = 1;
  ok &= mn[0] >= a[0];
  for (int i = 1; i <= n; i++) {
    mn[i] = min(2LL * (mn[i - 1] - a[i - 1]), mx[i]);
    ok &= mn[i] >= a[i];
    ans += mn[i];
  }

  ok &= mn[n] == a[n];

  if (ok) {
    cout << ans << endl;
  } else {
    cout << -1 << endl;
  }

  return 0;
}