121. Longest Palindromic Substring

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Input: s = "babad"

Output: "bab"

Explanation: The longest palindromic substring in "babad" is "bab". "aba" is also a valid answer.

Input: s = "cbbd"

Output: "bb"

Explanation: The longest palindromic substring in "cbbd" is "bb".

Input: s = "a"

Output: "a"

Explanation: If the input string has only one character, that character is the longest palindromic substring.

Input: s = "ac"

Output: "a"

Explanation: If there are no palindromic substrings of length greater than one, the first character is returned.

Time Complexity

O(n²)

Space Complexity

O(1)