E. Making Anti-Palindromestime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputYou are given a string s, consisting of lowercase English letters. In one operation, you are allowed to swap any two characters of the string s.A string s of length n is called an anti-palindrome, if s[i] \ne s[n - i + 1] for every i (1 \le i \le n). For example, the strings "codeforces", "string" are anti-palindromes, but the strings "abacaba", "abc", "test" are not.Determine the minimum number of operations required to make the string s an anti-palindrome, or output -1, if this is not possible.InputThe first line contains a single integer t (1 \le t \le 10^4) — the number of test cases. The description of the test cases follows.Each test case consists of two lines. The first line contains a single integer n (1 \le n \le 2 \cdot 10^5) — the length of the string s.The second line contains the string s, consisting of n lowercase English letters.The sum of n over all test cases does not exceed 2 \cdot 10^5.OutputFor each test case, output a single integer — the minimum number of operations required to make the string s an anti-palindrome, or -1 if this is not possible.ExampleInput
1010codeforces3abc10taarrrataa10dcbdbdcccc4wwww12cabbaccabaac10aadaaaaddc14aacdaaaacadcdc6abccba12dcbcaebacccdOutput
0
-1
1
1
-1
3
-1
2
2
2
NoteIn the first test case, the string "codeforces" is already an anti-palindrome, so the answer is 0.In the second test case, it can be shown that the string "abc" cannot be transformed into an anti-palindrome by performing the allowed operations, so the answer is -1.In the third test case, it is enough to swap the second and the fifth characters of the string "taarrrataa", and the new string "trararataa" will be an anti-palindrome, so the answer is 1.
1010codeforces3abc10taarrrataa10dcbdbdcccc4wwww12cabbaccabaac10aadaaaaddc14aacdaaaacadcdc6abccba12dcbcaebacccd
0 -1 1 1 -1 3 -1 2 2 2 
['greedy', 'math', 'strings', '*1600']