A14684 | Lexicographically Small Enough

You are given two strings $s$ and $t$ of equal length $n$ . In one move, you can swap any two adjacent characters of the string $s$ .

You need to find the minimal number of operations you need to make string $s$ lexicographically smaller than string $t$ .

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 $b$ .

The first line of input contains one integer $q$ ( $1 \le q \le 10\,000$ ): the number of test cases.

The first line of each test case contains a single integer $n$ ( $1 \le n \le 10^5$ ).

The second line of each test case contains the string $s$ consisting of $n$ lowercase English letters.

The third line of each test case contains the string $t$ consisting of $n$ lowercase English letters.

It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$ .

For each test case, print in a separate line the minimal number of operations you need to make string $s$ lexicographically smaller than string $t$ , or $-1$ , if it's impossible.