CF1617A.Forbidden Subsequence

You are given strings $S$ and $T$ , consisting of lowercase English letters. It is guaranteed that $T$ is a permutation of the string abc.

Find string $S'$ , the lexicographically smallest permutation of $S$ such that $T$ is not a subsequence of $S'$ .

String $a$ is a permutation of string $b$ if the number of occurrences of each distinct character is the same in both strings.

A string $a$ is a subsequence of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) elements.

A string $a$ is lexicographically smaller than a string $b$ if and only if one of the following holds:

• $a$ is a prefix of $b$ , but $a \ne b$ ;
• in the first position where $a$ and $b$ differ, the string $a$ has a letter that appears earlier in the alphabet than the corresponding letter in $b$ .

Each test contains multiple test cases. The first line contains a single integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases. Description of the test cases follows.

The first line of each test case contains a string $S$ ( $1 \le |S| \le 100$ ), consisting of lowercase English letters.

The second line of each test case contains a string $T$ that is a permutation of the string abc. (Hence, $|T| = 3$ ).

Note that there is no limit on the sum of $|S|$ across all test cases.

For each test case, output a single string $S'$ , the lexicographically smallest permutation of $S$ such that $T$ is not a subsequence of $S'$ .

In the first test case, both aaaabbc and aaaabcb are lexicographically smaller than aaaacbb, but they contain abc as a subsequence.

In the second test case, abccc is the smallest permutation of cccba and does not contain acb as a subsequence.

In the third test case, bcdis is the smallest permutation of dbsic and does not contain bac as a subsequence.