Problem
Decide whether text reads the same forwards and backwards, considering only letters and digits and ignoring case. Solve it recursively: compare the outer characters, then check the inside.
Implement is_palindrome_recursive(text).
Input
text: The text to check (ASCII characters).
Output
Return true for a palindrome, otherwise false.
Constraints
0 ≤ length ≤ 1,000
Examples
Input:
text = "Never odd or even"
Expected output:
expected = TrueInput:
std::string text = "Never odd or even";
Expected output:
bool expected = true;Input:
string text = "Never odd or even";
Expected output:
bool expected = true;Explanation
Letters only, lowercased: "neveroddoreven" reads the same both ways.
Input:
text = "code"
Expected output:
expected = FalseInput:
std::string text = "code";
Expected output:
bool expected = false;Input:
string text = "code";
Expected output:
bool expected = false;Explanation
"c" and "e" differ, so it is not a palindrome.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
Skip non-letter and non-digit characters before comparing the ends.
Hint 2
Compare the outer characters first, then recurse on the remaining middle part.
Hint 3
Handle empty and single-character cleaned substrings as palindromes.
Expected complexity
O(n) time, O(n) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.