Problem p02684 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define fr(i, j, k) for (i = j; i < (k); i++)
#define all(x) x.begin(), x.end()
#define el '\\n'
#define remax(a, b) a = max(a, b)
#define remin(a, b) a = min(a, b)
#define sz(x) int32_t(x.size())

typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpi;
// --------------------------------------------------------------------

const pii dxy[] = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};
const int mod = 1e9 + 7;
const int INF = 2e18;
const ld EPS = 1e-9;
const int NN = 2e5 + 2;

// string to_=================================================

vector<bool> vis(NN, 0);
vi d;

void solve() {
  int i = 0, j = 0, k = 0, n = 0, m = 0;
  cin >> n >> k;
  vi a(n);
  fr(i, 0, n) {
    cin >> a[i];
    a[i]--;
  }
  m = 0;
  while (!vis[m]) {
    d.pb(m);
    vis[m] = 1;
    m = a[m];
  }
  // m is visited
  int l = sz(d);
  for (i = 0; i < l; i++) {
    if (d[i] == m)
      break;
  }

  // d[i..l-1] is cycle
  int cyclen = l - i;
  if (k < l) {
    cout << d[k] + 1 << endl;
  } else {
    k = k - i;
    k %= cyclen;
    cout << d[k + i] + 1 << endl;
  }
  // cout << d[k]+1 << endl;
}

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T = 1;
  // cin >> T;
  for (int tc = 1; tc <= T; tc++) {
    solve();
  }
  return 0;
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define fr(i, j, k) for (i = j; i < (k); i++)
#define all(x) x.begin(), x.end()
#define el '\\n'
#define remax(a, b) a = max(a, b)
#define remin(a, b) a = min(a, b)
#define sz(x) int32_t(x.size())

typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpi;
// --------------------------------------------------------------------

const pii dxy[] = {{-1, 0}, {1, 0}, {0, 1}, {0, -1}};
const int mod = 1e9 + 7;
const int INF = 2e18;
const ld EPS = 1e-9;
const int NN = 1e5 + 2;

string to_string(string s) { return '"' + s + '"'; }
string to_string(const char *s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
template <typename A, typename B> string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A> string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}

#define TRACE

#ifdef TRACE
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif
//============================================================================

vector<bool> vis(NN, 0);
vi d;

void solve() {
  int i = 0, j = 0, k = 0, n = 0, m = 0;
  cin >> n >> k;
  vi a(n);
  fr(i, 0, n) {
    cin >> a[i];
    a[i]--;
  }
  m = 0;
  while (!vis[m]) {
    d.pb(m);
    vis[m] = 1;
    m = a[m];
  }
  // m is visited
  int l = sz(d);
  for (i = 0; i < l; i++) {
    if (d[i] == m)
      break;
  }

  // d[i..l-1] is cycle
  int cyclen = l - i;
  if (k < l) {
    cout << d[k] + 1 << endl;
  } else {
    k = k - i;
    k %= cyclen;
    cout << d[k + i] + 1 << endl;
  }
  // cout << d[k]+1 << endl;
}

int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T = 1;
  // cin >> T;
  for (int tc = 1; tc <= T; tc++) {
    solve();
  }
  return 0;
}