Nodes on Cycles

Difficulty: 1700 5000 ms 128 MB

graphs

Each node has exactly one outgoing edge (node i points to a_i). Count the nodes that lie on some cycle.

Input: the first line has N; the second line has the N successor values.

Output: the number of nodes on cycles.

Constraints:

• 1 ≤ N ≤ 10⁵
• 1 ≤ a_i ≤ N

Sample Tests

4
2 3 1 3

3

2
1 2

2

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