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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. using ll = long long;
  4. #define sz(st) int(st.size())
  5. #define all(st) st.begin(), st.end()
  6.  
  7.  
  8. void Solve()
  9. {
  10.     int n;
  11.     cin >> n;
  12.     vector<int> v(n + 1);
  13.     for (int i = 1; i <= n; i++) {
  14.         cin >> v[i];
  15.     }
  16.     vector < vector < int >>nxt(20, vector<int>(n + 1, n + 1));
  17.  
  18.     for (int i = 1;i <= n;i++) nxt[0][i] = v[i];
  19.  
  20.     for (int i = 1;i < 20;i++) {
  21.         for (int j = 1;j <= n;j++) {
  22.             nxt[i][j] = nxt[i - 1][nxt[i - 1][j]];
  23.         }
  24.     }
  25.     auto jump = [&](int i, int x) {
  26.         for (int j = 0; j < 20; j++) {
  27.             if (x & (1 << j)) {
  28.                 i = nxt[j][i];
  29.             }
  30.         }
  31.         return i;
  32.         };
  33.  
  34.     auto apply_k_times = [&](int k) {
  35.         vector < int > ret(n + 1);
  36.         for (int i = 1;i <= n;i++)
  37.             ret[jump(i, k - 1)] = 1;
  38.         return ret;
  39.         };
  40.  
  41.  
  42.     ll l = 2, r = n * 4, ans = n * 4;
  43.     while (l <= r) {
  44.         ll mid = (l + r) / 2;
  45.  
  46.         auto x = apply_k_times(mid);
  47.         auto x_1 = apply_k_times(mid - 1);
  48.  
  49.         if (x == x_1) {
  50.             ans = mid;
  51.             r = mid - 1;
  52.         }
  53.         else {
  54.             l = mid + 1;
  55.         }
  56.     }
  57.     cout << ans;
  58.  
  59.  
  60. }
  61.  
  62. signed main()
  63. {
  64. #if LOCAL
  65.     freopen("input.txt", "r", stdin);
  66.     freopen("output.txt", "w", stdout);
  67. #endif
  68.     ios_base::sync_with_stdio(false);
  69.     cin.tie(nullptr);
  70.     int t = 1;
  71.     cin >> t;
  72.     for (int tc = 1; tc <= t; tc++) {
  73.         Solve();
  74.         cout << "\n";
  75.     }
  76.     return 0;
  77. }
Success #stdin #stdout 0s 5288KB
comments (?)
stdin
copy 
5
2
2 1
5
2 3 4 5 1
5
2 1 4 2 3
5
4 1 1 5 4
10
4 3 9 1 6 7 9 10 10 3
stdout
copy 
2
2
5
4
5
https://ideone.com/wxzGEa
language:
C++ (gcc 8.3)
created:
7 days ago
visibility:
public

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