Problem p02684 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using ll = long long;
using ull = unsigned long long;
using namespace std;

#define FALSE printf("false\\n");
#define TRUE printf("true\\n");
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; (i) < ((int)(n)); ++(i))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define test(a)                                                                \\
  cout << "line:" << __LINE__ << "[" << (#a) << ": " << (a) << "]" << endl

const int INF = 1e9 + 7;
const ll INFL = 9 * 1e18;

// const int dx[4] = { 1, 0, -1, 0 };
// const int dy[4] = { 0, 1, 0, -1 };

const int dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const int dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};

ll inline digit(ll num) {
  int tmp = 0;
  while (num) {
    tmp++;
    num /= 10;
  }
  return tmp;
} // 桁数
template <typename T> inline void print(T &&x) {
  cout << x << endl;
} // 改行付き出力
template <typename T> inline T SUM(vector<T> vec) {
  return accumulate(all(vec), (T)0);
} // vectorの中身を全部足す
template <typename T> inline T digitSum(T num) {
  T sum = 0;
  while (num) {
    sum += num % 10;
    num /= 10;
  }
  return sum;
} // 各桁の和
template <typename T> inline T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
} // 最大公約数
template <typename T> inline T lcm(T a, T b) {
  T g = gcd(a, b);
  return a / g * b;
} // 最小公倍数
template <typename T> inline T power(T a, T b) {
  T tmp = 1;
  rep(i, b) { tmp *= a; }
  return tmp;
} // 累乗
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int ctoi(char c) { return c - '0'; }

// TODO: write
int main() {
#define int ll
  ll n, k;
  cin >> n >> k;
  vector<int> a(n);
  rep(i, n) cin >> a[i];

  if (n >= k) {
    int now = 0;
    rep(i, k) now = a[now] - 1;
    print(now + 1);
    return 0;
  }

  int visited[(int)1e6];
  rep(i, 1e6) visited[i] = 0;

  int now = 0;
  while (k--) {
    static int tmp = 0;
    now = a[now] - 1;
    if (visited[now])
      break;
    visited[now] = ++tmp;
  }

  ll cnt = 0;
  int next = now;
  while (true) {
    cnt++;
    next = a[next] - 1;
    if (next == now)
      break;
  }
  ll loop = k % cnt;
  while (loop--) {
    next = a[next] - 1;
  }
  print(next + 1);
  return 0;
}


Error: TLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using ll = long long;
using ull = unsigned long long;
using namespace std;

#define FALSE printf("false\\n");
#define TRUE printf("true\\n");
#define all(x) (x).begin(), (x).end()
#define rep(i, n) for (int i = 0; (i) < ((int)(n)); ++(i))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define test(a)                                                                \\
  cout << "line:" << __LINE__ << "[" << (#a) << ": " << (a) << "]" << endl

const int INF = 1e9 + 7;
const ll INFL = 9 * 1e18;

// const int dx[4] = { 1, 0, -1, 0 };
// const int dy[4] = { 0, 1, 0, -1 };

const int dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const int dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};

ll inline digit(ll num) {
  int tmp = 0;
  while (num) {
    tmp++;
    num /= 10;
  }
  return tmp;
} // 桁数
template <typename T> inline void print(T &&x) {
  cout << x << endl;
} // 改行付き出力
template <typename T> inline T SUM(vector<T> vec) {
  return accumulate(all(vec), (T)0);
} // vectorの中身を全部足す
template <typename T> inline T digitSum(T num) {
  T sum = 0;
  while (num) {
    sum += num % 10;
    num /= 10;
  }
  return sum;
} // 各桁の和
template <typename T> inline T gcd(T a, T b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
} // 最大公約数
template <typename T> inline T lcm(T a, T b) {
  T g = gcd(a, b);
  return a / g * b;
} // 最小公倍数
template <typename T> inline T power(T a, T b) {
  T tmp = 1;
  rep(i, b) { tmp *= a; }
  return tmp;
} // 累乗
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int ctoi(char c) { return c - '0'; }

// TODO: write
int main() {
  ll n, k;
  cin >> n >> k;
  vector<int> a(n);
  rep(i, n) cin >> a[i];
  int visited[(int)1e6];
  rep(i, 1e6) visited[i] = 0;

  int now = 0;
  while (k--) {
    static int tmp = 0;
    now = a[now] - 1;
    if (visited[now])
      break;
    visited[now] = ++tmp;
  }

  if (k == 0) {
    print(now + 1);
    return 0;
  }

  ll cnt = 0;
  int next = now;
  while (true) {
    cnt++;
    next = a[next] - 1;
    if (next == now)
      break;
  }
  ll loop = k % cnt;
  while (loop--) {
    next = a[next] - 1;
  }
  print(next + 1);
  return 0;
}