Problem p02684 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef HOME
#warning CHECK int:ll::INT_MAX:LLONG_MAX
#define maxn 20
#define debug(x...)                                                            \
  cerr << "[" << #x << "] = [";                                                \
  _print(x)
#else
#define maxn 2000006
#define gcd __gcd
#define debug(x...)
#endif

#define ff first
#define endl '\n'
#define ss second
#define inf 0x3f3f3f3f
#define MOD 1000000007
#define f(i, x, n) for (int i = x; i <= n; i++)
#define fr(i, x, n) for (int i = x; i >= n; i--)
struct _ {
  ios_base::Init i;
  _() { ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL); }
} _;

int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};

long long n, k;
long long st = 0;
vector<long long> a(maxn, 0);
vector<bool> vis(maxn, false);
vector<long long> path;

void dfs(long long curr) {
  if (vis[curr] == true) {
    st = curr;
    return;
  }
  vis[curr] = true;
  path.push_back(curr);

  dfs(a[curr]);
}
int main() {

  cin >> n >> k;
  for (long long i = 1; i <= n; i++)
    cin >> a[i];

  dfs(1);

  debug(path);

  vector<long long> new_path;
  for (auto i : path) {
    if (new_path.empty() == false)
      new_path.push_back(i);
    else if (i == st)
      new_path.push_back(i);
  }
  debug(new_path);
  long long x = (long long)path.size() - (long long)new_path.size();
  k -= x;
  k %= ((long long)new_path.size());

  cout << new_path[k];
  return 0;
}

Fixed submission:
#include <algorithm>
#include <assert.h>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;

void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }

template <typename T, typename V> void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T> void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x)
    cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V> void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v))
    cerr << ", ";
  _print(v...);
}
#ifdef HOME
#warning CHECK int:ll::INT_MAX:LLONG_MAX
#define maxn 20
#define debug(x...)                                                            \
  cerr << "[" << #x << "] = [";                                                \
  _print(x)
#else
#define maxn 2000006
#define gcd __gcd
#define debug(x...)
#endif

#define ff first
#define endl '\n'
#define ss second
#define inf 0x3f3f3f3f
#define MOD 1000000007
#define f(i, x, n) for (int i = x; i <= n; i++)
#define fr(i, x, n) for (int i = x; i >= n; i--)
struct _ {
  ios_base::Init i;
  _() { ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL); }
} _;

int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};

long long n, k;
long long st = 0;
vector<long long> a(maxn, 0);
vector<bool> vis(maxn, false);
vector<long long> path;

void dfs(long long curr) {
  if (vis[curr] == true) {
    st = curr;
    return;
  }
  vis[curr] = true;
  path.push_back(curr);

  dfs(a[curr]);
}
int main() {

  cin >> n >> k;
  for (long long i = 1; i <= n; i++)
    cin >> a[i];

  dfs(1);

  debug(path);

  vector<long long> new_path;
  for (auto i : path) {
    if (new_path.empty() == false)
      new_path.push_back(i);
    else if (i == st)
      new_path.push_back(i);
  }
  debug(new_path);
  long long x = (long long)path.size() - (long long)new_path.size();

  if (k < x) {
    cout << path[k];
    exit(0);
  }

  k -= x;
  k %= ((long long)new_path.size());

  cout << new_path[k];
  return 0;
}