Problem p02684 (C++)

Buggy submission (status: Runtime Error):
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
// #pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#endif

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits.h>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <time.h>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
#define int long long
// #define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v)                                                         \
  REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\n" : " ")
template <typename T1, typename T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <typename T1, typename T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef array<int, 3> arr3;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 1e9 + 7;
constexpr int MAX = 100050;
const double pi = acos(-1);
constexpr double EPS = 1e-12;
constexpr ll INF = 1e16;
void yes(bool c) {
  if (c)
    print("Yes");
  else
    print("No");
};

int dp[100010][70];
int nxt[100010];
void solve() {
  int N, K;
  cin >> N >> K;
  REP(i, N) {
    cin >> nxt[i];
    nxt[i]--;
  }
  REP(i, N) { dp[i][0] = nxt[i]; }
  REP(k, 61) {
    REP(i, N) { dp[i][k + 1] = dp[dp[i][k]][k]; }
  }
  int now = 0;
  REPR(i, 60) {
    if (K & (1LL << i)) {
      now = dp[now][i];
    }
  }
  print(now + 1);
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  // int q; cin >> q;
  // while (q--)
  solve();
}


Fixed submission:
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
// #pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#endif

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits.h>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <time.h>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
#define int long long
// #define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v)                                                         \
  REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\n" : " ")
template <typename T1, typename T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <typename T1, typename T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef array<int, 3> arr3;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 1e9 + 7;
constexpr int MAX = 100050;
const double pi = acos(-1);
constexpr double EPS = 1e-12;
constexpr ll INF = 1e16;
void yes(bool c) {
  if (c)
    print("Yes");
  else
    print("No");
};

int dp[200010][70];
int nxt[200010];
void solve() {
  int N, K;
  cin >> N >> K;
  REP(i, N) {
    cin >> nxt[i];
    nxt[i]--;
  }
  REP(i, N) { dp[i][0] = nxt[i]; }
  REP(k, 61) {
    REP(i, N) { dp[i][k + 1] = dp[dp[i][k]][k]; }
  }
  int now = 0;
  REPR(i, 60) {
    if (K & (1LL << i)) {
      now = dp[now][i];
    }
  }
  print(now + 1);
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  // int q; cin >> q;
  // while (q--)
  solve();
}