Problem p03061 (C++)

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

using ll = int64_t;
#define int ll

#define FOR(i, a, b) for (int i = int(a); i < int(b); i++)
#define REP(i, b) FOR(i, 0, b)
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(x) x.begin(), x.end()

using pi = pair<int, int>;
using vi = vector<int>;
using ld = long double;

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << "," << p.second << ")";
  return os;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  REP(i, (int)v.size()) {
    if (i)
      os << ",";
    os << v[i];
  }
  os << "}";
  return os;
}

ll read() {
  ll i;
  scanf("%" SCNd64, &i);
  return i;
}

void printSpace() { printf(" "); }

void printEoln() { printf("\n"); }

void print(ll x, int suc = 1) {
  printf("%" PRId64, x);
  if (suc == 1)
    printEoln();
  if (suc == 2)
    printSpace();
}

string readString() {
  static char buf[3341000];
  scanf("%s", buf);
  return string(buf);
}

char *readCharArray() {
  static char buf[3341000];
  static int bufUsed = 0;
  char *ret = buf + bufUsed;
  scanf("%s", ret);
  bufUsed += strlen(ret) + 1;
  return ret;
}

template <class T, class U> void chmax(T &a, U b) {
  if (a < b)
    a = b;
}

template <class T, class U> void chmin(T &a, U b) {
  if (b < a)
    a = b;
}

template <class T> T Sq(const T &t) { return t * t; }

const int mod = 1e9 + 7;

int gcd(int x, int y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}

signed main() {
  int n;
  cin >> n;
  vi a;
  REP(i, n) { a.PB(read()); }
  vi l(n), r(n);
  REP(i, n - 1) { l[i + 1] = gcd(l[i], a[i]); }
  for (int i = n - 1; i <= 1; i--)
    r[i - 1] = gcd(r[i], a[i]);
  int ans = 1;
  REP(i, n) { chmax(ans, gcd(l[i], r[i])); }
  print(ans);
}


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

using ll = int64_t;
#define int ll

#define FOR(i, a, b) for (int i = int(a); i < int(b); i++)
#define REP(i, b) FOR(i, 0, b)
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(x) x.begin(), x.end()

using pi = pair<int, int>;
using vi = vector<int>;
using ld = long double;

template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << "(" << p.first << "," << p.second << ")";
  return os;
}

template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  REP(i, (int)v.size()) {
    if (i)
      os << ",";
    os << v[i];
  }
  os << "}";
  return os;
}

ll read() {
  ll i;
  scanf("%" SCNd64, &i);
  return i;
}

void printSpace() { printf(" "); }

void printEoln() { printf("\n"); }

void print(ll x, int suc = 1) {
  printf("%" PRId64, x);
  if (suc == 1)
    printEoln();
  if (suc == 2)
    printSpace();
}

string readString() {
  static char buf[3341000];
  scanf("%s", buf);
  return string(buf);
}

char *readCharArray() {
  static char buf[3341000];
  static int bufUsed = 0;
  char *ret = buf + bufUsed;
  scanf("%s", ret);
  bufUsed += strlen(ret) + 1;
  return ret;
}

template <class T, class U> void chmax(T &a, U b) {
  if (a < b)
    a = b;
}

template <class T, class U> void chmin(T &a, U b) {
  if (b < a)
    a = b;
}

template <class T> T Sq(const T &t) { return t * t; }

const int mod = 1e9 + 7;

int gcd(int x, int y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}

signed main() {
  int n;
  cin >> n;
  vi a;
  REP(i, n) { a.PB(read()); }
  vi l(n), r(n);
  REP(i, n - 1) { l[i + 1] = gcd(l[i], a[i]); }
  for (int i = n - 1; i >= 1; i--)
    r[i - 1] = gcd(r[i], a[i]);
  int ans = 1;
  REP(i, n) { chmax(ans, gcd(l[i], r[i])); }
  print(ans);
}