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

/*
    Author : Nishant Gupta 2.0
*/
#include <bits/stdc++.h>

#define LL long long int
#define getcx getchar_unlocked
#define X first
#define Y second
#define PB push_back
#define MP make_pair
#define MAX 200005
#define MOD 1000000007
#define INF 0x3f3f3f3f
#define INFL (LL(1e18))
#define rep(i, a, n) for (i = a; i < n; i++)
#define rev(i, a, n) for (i = a; i >= n; i--)
#define MSV(A, a) memset(A, a, sizeof(A))
#define rep_itr(itr, c) for (itr = (c).begin(); itr != (c).end(); itr++)

using namespace std;

inline void inp(int &n) {
  n = 0;
  int ch = getcx();
  int sign = 1;
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      sign = -1;
    ch = getcx();
  }
  while (ch >= '0' && ch <= '9')
    n = (n << 3) + (n << 1) + ch - '0', ch = getcx();
  n = n * sign;
}

inline void inp1(LL &n) {
  n = 0;
  LL ch = getcx();
  LL sign = 1;
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      sign = -1;
    ch = getcx();
  }
  while (ch >= '0' && ch <= '9')
    n = (n << 3) + (n << 1) + ch - '0', ch = getcx();
  n = n * sign;
}

vector<int> adj[MAX];
int st, e;
int vis[MAX];
int cnt;
int offset;
void dfs(int node, int p) {
  if (vis[node]) {
    st = node;
    e = p;
    offset = vis[node] - 1;
    return;
  }

  vis[node] = cnt++;

  for (int i = 0; i < adj[node].size(); i++) {
    dfs(adj[node][i], node);
  }
  return;
}

vector<int> chain;
void get_chain(int node, int dest) {
  if (node == dest) {
    chain.PB(dest);
    return;
  }

  chain.PB(node);
  for (int i = 0; i < adj[node].size(); i++) {
    get_chain(adj[node][i], dest);
  }
}

int main() {
  LL n, k;
  int i;
  cin >> n >> k;

  int x;
  for (i = 1; i <= n; i++) {
    cin >> x;
    adj[i].PB(x);
  }
  cnt = 1;

  dfs(1, 1);

  if (k < offset) {
    get_chain(1, st);
    cout << chain[k] << endl;
    return 0;
  }
  k -= offset;
  get_chain(st, e);
  int cn = chain.size();
  k = k % cn;

  cout << chain[k] << endl;

  return 0;
}


Error: 0

Fixed submission:

/*
    Author : Nishant Gupta 2.0
*/
#include <bits/stdc++.h>

#define LL long long int
#define getcx getchar_unlocked
#define X first
#define Y second
#define PB push_back
#define MP make_pair
#define MAX 200005
#define MOD 1000000007
#define INF 0x3f3f3f3f
#define INFL (LL(1e18))
#define rep(i, a, n) for (i = a; i < n; i++)
#define rev(i, a, n) for (i = a; i >= n; i--)
#define MSV(A, a) memset(A, a, sizeof(A))
#define rep_itr(itr, c) for (itr = (c).begin(); itr != (c).end(); itr++)

using namespace std;

inline void inp(int &n) {
  n = 0;
  int ch = getcx();
  int sign = 1;
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      sign = -1;
    ch = getcx();
  }
  while (ch >= '0' && ch <= '9')
    n = (n << 3) + (n << 1) + ch - '0', ch = getcx();
  n = n * sign;
}

inline void inp1(LL &n) {
  n = 0;
  LL ch = getcx();
  LL sign = 1;
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      sign = -1;
    ch = getcx();
  }
  while (ch >= '0' && ch <= '9')
    n = (n << 3) + (n << 1) + ch - '0', ch = getcx();
  n = n * sign;
}

vector<int> adj[MAX];
int st, e;
int vis[MAX];
int cnt;
int offset;
void dfs(int node, int p) {
  if (vis[node]) {
    st = node;
    e = p;
    offset = vis[node] - 1;
    return;
  }

  vis[node] = cnt++;

  for (int i = 0; i < adj[node].size(); i++) {
    dfs(adj[node][i], node);
  }
  return;
}

vector<int> chain;
void get_chain(int node, int dest) {
  if (node == dest) {
    chain.PB(dest);
    return;
  }

  chain.PB(node);
  for (int i = 0; i < adj[node].size(); i++) {
    get_chain(adj[node][i], dest);
  }
}

int main() {
  LL n, k;
  int i;
  cin >> n >> k;

  int x;
  for (i = 1; i <= n; i++) {
    cin >> x;
    adj[i].PB(x);
  }
  cnt = 1;

  dfs(1, 1);

  k -= offset;
  get_chain(st, e);
  int cn = chain.size();
  k = k % cn;

  cout << chain[k] << endl;

  return 0;
}