CF1822E Making Anti-Palindromes

You 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.

N/A

N/A

In 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 $ .