Problem p02641 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <numeric>
#include <queue>
#include <string>
#include <utility>
#include <vector>

using namespace std;
#define ALL(a) (a).begin(), (a).end()
#define REP(i, n) for (size_t i = 0; i < (n); i++)
#define nvec(T, v, n)                                                          \\
  vector<T> v(n);                                                              \\
  REP(i, n) { cin >> (v)[i]; }
#define npairs(T1, T2, v, n)                                                   \\
  vector<pair<T1, T2>> v(n);                                                   \\
  REP(i, n) { cin >> v[i].first >> v[i].second; }
#define ntuples(T1, T2, T3, v, n)                                              \\
  vector<tuple<T1, T2, T3>> v(n);                                              \\
  REP(i, n) { cin >> get<0>(v[i]) >> get<1>(v[i]) >> get<2>(v[i]); }
#define vec2d(T, v, m, n) vector<vector<T>>(v)(m, vector<T>(n))
#define nvec2d(T, v, m, n)                                                     \\
  vec2d(T, v, m, n);                                                           \\
  REP(j, m) {                                                                  \\
    REP(i, n) { cin >> (v[j])[i]; }                                            \\
  }

#define min_index(v) size_t(min_element(all(v)) - (v).begin())
#define max_index(v) size_t(max_element(all(v)) - (v).begin())
#define min_e(v) *min_element(ALL(v))
#define max_e(v) *max_element(ALL(v))

#define count_le(v, a) size_t(upper_bound(ALL(v), a) - (v).begin())
#define count_lt(v, a) size_t(lower_bound(ALL(v), a) - (v).begin())
#define count_ge(v, a) size_t((v).end() - lower_bound(ALL(v), a))
#define count_gt(v, a) size_t((v).end() - upper_bound(ALL(v), a))

#define order(neq_sl) [](const auto s, const auto l) { return neq_sl; }
#define make_lr(v, type, l, r)                                                 \\
  vector<type> l(n + 1), r(n + 1);                                             \\
  FOR(i, n) {                                                                  \\
    l[i + 1] = l[i] + v[i];                                                    \\
    r[i + 1] = r[i] + v[n - 1 - i];                                            \\
  }

#define acm accumulate
#define SUM(v) accumulate(ALL(v), 0l)
#define SORT(v) sort(ALL(v))

#define GCD(v) gcd(ALL(v), 0l)

/*template <typename T>
T gcd(T a, T b) {
    if (a > b) swap(a, b);
    if (a == 0) return b;
    return gcd(b%a, a);
}
template <typename InputItr, typename T>
T gcd(InputItr first, InputItr last, T init) {
    for (; first != last; ++first) init = gcd(init, *first);
    return init;
}*/

template <typename T> using vec = vector<T>;

template <typename T> using vvec = vector<vector<T>>;

int main() {
  int x, n;
  cin >> x >> n;
  nvec(int, p, n);
  vec<pair<int, int>> q;
  for (int i = 0; i < 102; i++) {
    bool a = 1;
    for (int j = 0; j < n; j++) {
      if (i == p[j])
        a = 0;
    }
    if (a == 1)
      q.push_back(make_pair(abs(x - i), i));
  }
  SORT(q);
  cout << q[0].second;
}

/* きょむ〜 */


Error: WA

Fixed submission:

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <numeric>
#include <queue>
#include <string>
#include <utility>
#include <vector>

using namespace std;
#define ALL(a) (a).begin(), (a).end()
#define REP(i, n) for (size_t i = 0; i < (n); i++)
#define nvec(T, v, n)                                                          \\
  vector<T> v(n);                                                              \\
  REP(i, n) { cin >> (v)[i]; }
#define npairs(T1, T2, v, n)                                                   \\
  vector<pair<T1, T2>> v(n);                                                   \\
  REP(i, n) { cin >> v[i].first >> v[i].second; }
#define ntuples(T1, T2, T3, v, n)                                              \\
  vector<tuple<T1, T2, T3>> v(n);                                              \\
  REP(i, n) { cin >> get<0>(v[i]) >> get<1>(v[i]) >> get<2>(v[i]); }
#define vec2d(T, v, m, n) vector<vector<T>>(v)(m, vector<T>(n))
#define nvec2d(T, v, m, n)                                                     \\
  vec2d(T, v, m, n);                                                           \\
  REP(j, m) {                                                                  \\
    REP(i, n) { cin >> (v[j])[i]; }                                            \\
  }

#define min_index(v) size_t(min_element(all(v)) - (v).begin())
#define max_index(v) size_t(max_element(all(v)) - (v).begin())
#define min_e(v) *min_element(ALL(v))
#define max_e(v) *max_element(ALL(v))

#define count_le(v, a) size_t(upper_bound(ALL(v), a) - (v).begin())
#define count_lt(v, a) size_t(lower_bound(ALL(v), a) - (v).begin())
#define count_ge(v, a) size_t((v).end() - lower_bound(ALL(v), a))
#define count_gt(v, a) size_t((v).end() - upper_bound(ALL(v), a))

#define order(neq_sl) [](const auto s, const auto l) { return neq_sl; }
#define make_lr(v, type, l, r)                                                 \\
  vector<type> l(n + 1), r(n + 1);                                             \\
  FOR(i, n) {                                                                  \\
    l[i + 1] = l[i] + v[i];                                                    \\
    r[i + 1] = r[i] + v[n - 1 - i];                                            \\
  }

#define acm accumulate
#define SUM(v) accumulate(ALL(v), 0l)
#define SORT(v) sort(ALL(v))

#define GCD(v) gcd(ALL(v), 0l)

/*template <typename T>
T gcd(T a, T b) {
    if (a > b) swap(a, b);
    if (a == 0) return b;
    return gcd(b%a, a);
}
template <typename InputItr, typename T>
T gcd(InputItr first, InputItr last, T init) {
    for (; first != last; ++first) init = gcd(init, *first);
    return init;
}*/

template <typename T> using vec = vector<T>;

template <typename T> using vvec = vector<vector<T>>;

int main() {
  int x, n;
  cin >> x >> n;
  nvec(int, p, n);
  vec<pair<int, int>> q;
  for (int i = 1; i < 101; i++) {
    bool a = 1;
    for (int j = 0; j < n; j++) {
      if (i == p[j])
        a = 0;
    }
    if (a == 1)
      q.push_back(make_pair(abs(x - i), i));
  }
  SORT(q);
  cout << q[0].second;
}

/* きょむ〜 */