Score : $200$ points

问题描述

有 $N$ 名人员，其ID分别为 $1$, $2$, $\ldots$, 和 $N$。

按照顺序，每个人员 $1$、人员 $2$、$\ldots$ 以及人员 $N$ 各执行以下操作一次：

• 若人员 $i$ 的ID尚未被叫出，则叫出人员 $A_i$ 的ID。

请按 升序 列举直至最后从未被叫出过ID的所有人员的ID。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

There are $N$ people whose IDs are $1$, $2$, $\ldots$, and $N$.

Each of person $1$, person $2$, $\ldots$, and person $N$ performs the following action once in this order:

• If person $i$'s ID has not been called out yet, call out person $A_i$'s ID.

Enumerate the IDs of all the people whose IDs are never called out until the end in ascending order.

Constraints

• $2 \leq N \leq 2 \times 10^5$
• $1 \leq A_i \leq N$
• $A_i \neq i$
• All values in the input are integers.

Input

The input is given from Standard Input in the following format:

$N$

$A_1$ $A_2$ $\ldots$ $A_N$

Output

Enumerate the IDs of all the people whose IDs are not called out until the end in ascending order in the following format:

$K$

$X_1$ $X_2$ $\ldots$ $X_K$

In other words, the first line should contain the number of people, $K$, whose IDs are never called out until the end; the second line should contain the sequence $(X_1, X_2, \ldots, X_K)$ of IDs of such people in ascending order, with spaces in between.

Sample Input 1

5
3 1 4 5 4

Sample Output 1

2
2 4

The five people's actions are as follows.

• Person $1$'s ID has not been called out yet, so person $1$ calls out person $3$'s ID.
• Person $2$'s ID has not been called out yet, so person $2$ calls out person $1$'s ID.
• Person $3$'s ID has already been called out by person $1$, so nothing happens.
• Person $4$'s ID has not been called out yet, so person $4$ calls out person $5$'s ID.
• Person $5$'s ID has already been called out by person $4$, so nothing happens.

Therefore, person $2$ and $4$'s IDs are not called out until the end.

Sample Input 2

20
9 7 19 7 10 4 13 9 4 8 10 15 16 3 18 19 12 13 2 12

Sample Output 2

10
1 2 5 6 8 11 14 17 18 20

update @ 2024/3/10 12:12:06