Problem p02684 (C++)

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

#define ff first
#define ss second
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \
  int x;                                                                       \
  cin >> x;                                                                    \
  while (x--)
#define FIO                                                                    \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);                                                                  \
  cout.tie(0)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

int32_t main() {
  FIO;
  int n, k;
  cin >> n >> k;
  vi v;
  v.pb(1);

  mk(arr, n + 1, int);

  for (int i = 1; i <= n; ++i)
    cin >> arr[i];

  int cur = arr[1];
  set<int> vis;
  vis.insert(1);

  while (!vis.count(cur)) {
    v.pb(cur);
    vis.insert(cur);
    cur = arr[cur];
  }

  int id;

  for (int i = 0; i < v.size(); ++i) {
    if (cur == v[i]) {
      id = i;
      break;
    }
  }

  if (k < id) {
    cout << v[k] << '\n';
  }

  vi tmp;

  for (int i = id; i < v.size(); ++i)
    tmp.pb(v[i]);

  v = tmp;
  k -= id;

  n = v.size();
  k %= n;

  cout << v[k] << '\n';
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;

#define ff first
#define ss second
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int, int>
#define vi vector<int>
#define mii map<int, int>
#define pqb priority_queue<int>
#define pqs priority_queue<int, vi, greater<int>>
#define setbits(x) __builtin_popcountll(x)
#define zrobits(x) __builtin_ctzll(x)
#define mod 1000000007
#define inf 1e18
#define ps(x, y) fixed << setprecision(y) << x
#define mk(arr, n, type) type *arr = new type[n];
#define w(x)                                                                   \
  int x;                                                                       \
  cin >> x;                                                                    \
  while (x--)
#define FIO                                                                    \
  ios_base::sync_with_stdio(0);                                                \
  cin.tie(0);                                                                  \
  cout.tie(0)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

typedef tree<int, null_type, less<int>, rb_tree_tag,
             tree_order_statistics_node_update>
    pbds;

int32_t main() {
  FIO;
  int n, k;
  cin >> n >> k;
  vi v;
  v.pb(1);

  mk(arr, n + 1, int);

  for (int i = 1; i <= n; ++i)
    cin >> arr[i];

  int cur = arr[1];
  set<int> vis;
  vis.insert(1);

  while (!vis.count(cur)) {
    v.pb(cur);
    vis.insert(cur);
    cur = arr[cur];
  }

  int id;

  for (int i = 0; i < v.size(); ++i) {
    if (cur == v[i]) {
      id = i;
      break;
    }
  }

  if (k < id) {
    cout << v[k] << '\n';
    return 0;
  }

  vi tmp;

  for (int i = id; i < v.size(); ++i)
    tmp.pb(v[i]);

  v = tmp;
  k -= id;

  n = v.size();
  k %= n;

  cout << v[k] << '\n';
  return 0;
}