You are given a string s of length n consisting of lowercase English letters.
Return the smallest index i such that s[i] == s[n - i - 1].
If no such index exists, return -1.
Example 1:
Input: s = "abcacbd"
Output: 1
Explanation:
At index i = 1, s[1] and s[5] are both 'b'.
No smaller index satisfies the condition, so the answer is 1.
Example 2:
Input: s = "abc"
Output: 1
Explanation:
At index i = 1, the two compared positions coincide, so both characters are 'b'.
No smaller index satisfies the condition, so the answer is 1.
Example 3:
Input: s = "abcdab"
Output: -1
Explanation:
For every index i, the characters at positions i and n - i - 1 are different.
Therefore, no valid index exists, so the answer is -1.
Constraints:
1 <= n == s.length <= 100s consists of lowercase English letters.