String LCM

2000ms

262144K

Description:

Let's define a multiplication operation between a string $$$a$$$ and a positive integer $$$x$$$: $$$a \cdot x$$$ is the string that is a result of writing $$$x$$$ copies of $$$a$$$ one after another. For example, "abc" $$$\cdot~2~=$$$ "abcabc", "a" $$$\cdot~5~=$$$ "aaaaa".

A string $$$a$$$ is divisible by another string $$$b$$$ if there exists an integer $$$x$$$ such that $$$b \cdot x = a$$$. For example, "abababab" is divisible by "ab", but is not divisible by "ababab" or "aa".

LCM of two strings $$$s$$$ and $$$t$$$ (defined as $$$LCM(s, t)$$$) is the shortest non-empty string that is divisible by both $$$s$$$ and $$$t$$$.

You are given two strings $$$s$$$ and $$$t$$$. Find $$$LCM(s, t)$$$ or report that it does not exist. It can be shown that if $$$LCM(s, t)$$$ exists, it is unique.

Input:

The first line contains one integer $$$q$$$ ($$$1 \le q \le 2000$$$) — the number of test cases.

Each test case consists of two lines, containing strings $$$s$$$ and $$$t$$$ ($$$1 \le |s|, |t| \le 20$$$). Each character in each of these strings is either 'a' or 'b'.

Output:

For each test case, print $$$LCM(s, t)$$$ if it exists; otherwise, print -1. It can be shown that if $$$LCM(s, t)$$$ exists, it is unique.

Sample Input:

3
baba
ba
aa
aaa
aba
ab

Sample Output:

baba
aaaaaa
-1

Note:

In the first test case, "baba" = "baba" $$$\cdot~1~=$$$ "ba" $$$\cdot~2$$$.

In the second test case, "aaaaaa" = "aa" $$$\cdot~3~=$$$ "aaa" $$$\cdot~2$$$.

Informação

Provedor Codeforces

Código CF1473B