Autosynthesis
Description
Chaneka writes down an array $a$ of $n$ positive integer elements. Initially, all elements are not circled. In one operation, Chaneka can circle an element. It is possible to circle the same element more than once.
After doing all operations, Chaneka makes a sequence $r$ consisting of all uncircled elements of $a$ following the order of their indices.
Chaneka also makes another sequence $p$ such that its length is equal to the number of operations performed and $p_i$ is the index of the element that is circled in the $i$-th operation.
Chaneka wants to do several operations such that sequence $r$ is equal to sequence $p$. Help her achieve this, or report if it is impossible! Note that if there are multiple solutions, you can print any of them.
翻译
给定一个长度为 的序列 。
你可以对这个序列进行任意次操作，每次操作选择一个下标 ，并圈住下标为 的数 。可以多次圈一个数。
请构造出一组操作方案，使得操作选出的下标序列 等于没有被圈过的数构成的序列 。
请注意，下标序列和没有被圈过的数的序列皆有序，后者按照原序列顺序依次排列。
Input
The first line contains a single integer $n$ ($1 \leq n \leq 2\cdot10^5$) — the size of array $a$.
The second line contains $n$ integers $a_1,a_2,a_3,\ldots,a_n$ ($1\leq a_i\leq n$).
Output
A single line containing $-1$ if it is impossible.
Otherwise, the output consists of two lines. The first line contains an integer $z$ representing the number of operations performed. The second line contains $z$ integers, the $i$-th integer represents the index of the element circled in the $i$-th operation. If there are multiple solutions, you can print any of them.
5
3 4 2 2 3
3
1 2 3
3
3 2 3
-1
Note
In the first example, doing the operations like the example output gives the following results:
- Element $a_2$ gets circled $1$ time.
- Element $a_3$ gets circled $2$ times.
- The uncircled elements (ordered by their indices) are $a_1$, $a_4$, and $a_5$. So $r=[3,2,3]$.
- $p=[3,2,3]$
Therefore, $r=p$.
In the second example, it is impossible.
相关
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