QOJ.ac

QOJ

Límite de tiempo: 1 s Límite de memoria: 512 MB Puntuación total: 100

#1770. Palindrome

Estadísticas

Given a positive integer $n$ and an integer sequence $a_1, a_2, \dots, a_{2n}$, where each of the numbers $1, 2, \dots, n$ appears exactly twice in these $2n$ numbers. We perform $2n$ operations to create a sequence $b_1, b_2, \dots, b_{2n}$ of the same length. Initially, $b$ is an empty sequence. In each step, we can perform one of the following two operations:

  1. Add the first element of sequence $a$ to the end of $b$, and remove it from $a$.
  2. Add the last element of sequence $a$ to the end of $b$, and remove it from $a$.

Our goal is to make $b$ a palindrome, i.e., $b_i = b_{2n+1-i}$ for all $1 \le i \le n$. Determine if this goal can be achieved. If it can, output the lexicographically smallest operation sequence, as specified in the Output section.

Input

The input is read from the file palin.in. Each test case contains multiple test data. The first line of the input contains an integer $T$, representing the number of test cases. The first line of each test case contains a positive integer $n$, and the second line contains $2n$ space-separated integers $a_1, a_2, \dots, a_{2n}$.

Output

The output is written to the file palin.out. For each test case, output the answer on a single line. If it is impossible to generate a palindrome sequence, output -1. Otherwise, output a string of length $2n$ consisting of characters L or R (without spaces), where L represents operation 1 (removing the first element) and R represents operation 2 (removing the last element). You must output the lexicographically smallest string among all valid schemes. The lexicographical comparison rule is as follows: a string $s_{1 \dots 2n}$ is lexicographically smaller than $t_{1 \dots 2n}$ if and only if there exists an index $1 \le k \le 2n$ such that $\forall 1 \le i < k$, $s_i = t_i$ and $s_k < t_k$.

Examples

Input 1

2
5
4 1 2 4 5 3 1 2 3 5
3
3 2 1 2 1 3

Output 1

LRRLLRRRRL
-1

Note 1

In the first test case, the generated sequence $b$ is $4, 5, 3, 1, 2, 2, 1, 3, 5, 4$, which is a palindrome. Another possible operation scheme is LRRLLRRRRR, but it is lexicographically larger than the answer.

Examples 2

See palin/palin2.in and palin/palin2.ans in the contestant's directory.

Constraints

Let $\sum n$ denote the sum of $n$ over all $T$ test cases. For all test cases, it is guaranteed that $1 \le T \le 100$, $1 \le n$, and $\sum n \le 5 \times 10^5$.

Test Case ID $T$ $n$ $\sum n$ Special Property
$1 \sim 7$ None
$8 \sim 10$
$11 \sim 12$
$13 \sim 15$
$16 \sim 17$ $= 1$ $\le 5 \times 10^5$ $\le 5 \times 10^5$ None
$18 \sim 20$ $\le 100$ $\le 5 \times 10^5$ $\le 5 \times 10^5$ Yes
$21 \sim 25$ None

Special property: If we remove two adjacent and equal numbers from $a$ each time, there exists a way to empty the sequence (e.g., $a = [1, 2, 2, 1]$).

Discussions

About Discussions

The discussion section is only for posting: General Discussions (problem-solving strategies, alternative approaches), and Off-topic conversations.

This is NOT for reporting issues! If you want to report bugs or errors, please use the Issues section below.

Open Discussions 0
No discussions in this category.

Issues

About Issues

If you find any issues with the problem (statement, scoring, time/memory limits, test cases, etc.), you may submit an issue here. A problem moderator will review your issue.

Guidelines:

  1. This is not a place to publish discussions, editorials, or requests to debug your code. Issues are only visible to you and problem moderators.
  2. Do not submit duplicated issues.
  3. Issues must be filed in English or Chinese only.
Active Issues 0
No issues in this category.
Closed/Resolved Issues 0
No issues in this category.