A13523 | Rotating Substrings

You are given two strings $s$ and $t$ , each of length $n$ and consisting of lowercase Latin alphabets. You want to make $s$ equal to $t$ .

You can perform the following operation on $s$ any number of times to achieve it —

- Choose any substring of $s$ and rotate it clockwise once, that is, if the selected substring is $s[l,l+1...r]$ , then it becomes $s[r,l,l + 1 ... r - 1]$ . All the remaining characters of $s$ stay in their position. For example, on rotating the substring $[2,4]$ , string "abcde" becomes "adbce".

A string $a$ is a substring of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) characters from the beginning and several (possibly, zero or all) characters from the end.

Find the minimum number of operations required to convert $s$ to $t$ , or determine that it's impossible.

The first line of the input contains a single integer $t$ $(1\leq t \leq 2000)$ — the number of test cases. The description of the test cases follows.

The first line of each test case contains a single integer $n$ $(1\leq n \leq 2000)$ — the length of the strings.

The second and the third lines contain strings $s$ and $t$ respectively.

The sum of $n$ over all the test cases does not exceed $2000$ .

For each test case, output the minimum number of operations to convert $s$ to $t$ . If it is not possible to convert $s$ to $t$ , output $-1$ instead.