Problem p02641 (C++)

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

typedef long long ll;
#define ar array
#define vi vector<int>
#define vvi vector<vector<int>>
#define vll vector<long long>
#define fork(i, n) for (ll i = 0; i < (n); i++)
#define forn for (ll i = 0; i < (n); i++)
#define fori(i, k, n) for (ll i = k; i < (n); i++)
#define all(x) (x).begin(), (x).end()
#define en '\n'
#define FILL(x, v) memset(x, v, sizeof(x))
#define pb push_back
#define fast                                                                   \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);

template <typename A, typename B> inline void chmin(A &a, B b) {
  if (a > b)
    a = b;
}
template <typename A, typename B> inline void chmax(A &a, B b) {
  if (a < b)
    a = b;
}
template <typename T> void print(vector<T> &a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << ' ';
  cout << en;
}
template <typename T> void print(deque<T> &a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << ' ';
  cout << en;
}
template <typename T> void print(vector<vector<T>> &a) {
  for (int i = 0; i < a.size(); i++) {
    for (int j = 0; j < a[i].size(); j++)
      cout << a[i][j] << ' ';
    cout << en;
  }
}

int main() {
  fast;
  int x, n;
  cin >> x >> n;
  vector<bool> a(n + 1, 0);
  if (n == 0) {
    cout << x << en;
    return 0;
  }
  forn {
    int t;
    cin >> t;
    if (t < 0)
      continue;
    a[t] = 1;
  }
  int ans, cur = 1e9 + 5;
  for (int i = x + n; i >= x - n; i--) {
    if (a[i])
      continue;
    // cout << i << en;
    int dif = abs(i - x);
    if (dif <= cur) {
      cur = dif;
      ans = i;
    }
  }
  cout << ans << en;
}

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

typedef long long ll;
#define ar array
#define vi vector<int>
#define vvi vector<vector<int>>
#define vll vector<long long>
#define fork(i, n) for (ll i = 0; i < (n); i++)
#define forn for (ll i = 0; i < (n); i++)
#define fori(i, k, n) for (ll i = k; i < (n); i++)
#define all(x) (x).begin(), (x).end()
#define en '\n'
#define FILL(x, v) memset(x, v, sizeof(x))
#define pb push_back
#define fast                                                                   \
  ios::sync_with_stdio(false);                                                 \
  cin.tie(NULL);                                                               \
  cout.tie(NULL);

template <typename A, typename B> inline void chmin(A &a, B b) {
  if (a > b)
    a = b;
}
template <typename A, typename B> inline void chmax(A &a, B b) {
  if (a < b)
    a = b;
}
template <typename T> void print(vector<T> &a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << ' ';
  cout << en;
}
template <typename T> void print(deque<T> &a) {
  for (int i = 0; i < a.size(); i++)
    cout << a[i] << ' ';
  cout << en;
}
template <typename T> void print(vector<vector<T>> &a) {
  for (int i = 0; i < a.size(); i++) {
    for (int j = 0; j < a[i].size(); j++)
      cout << a[i][j] << ' ';
    cout << en;
  }
}

int main() {
  fast;
  int x, n;
  cin >> x >> n;
  vector<bool> a(n + 1, 0);
  if (n == 0) {
    cout << x << en;
    return 0;
  }
  forn {
    int t;
    cin >> t;
    if (t < 0)
      continue;
    a[t] = 1;
  }
  int ans, cur = 1e9 + 5;
  for (int i = x + n; i >= 0 && i >= x - n; i--) {
    if (a[i])
      continue;
    // cout << i << en;
    int dif = abs(i - x);
    if (dif <= cur) {
      cur = dif;
      ans = i;
    }
  }
  cout << ans << en;
}