CF1616E 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.