Palindrome check
A puzzle feature checks whether a phrase reads the same backwards.
- Compare letters and digits only — skip spaces and punctuation.
- Case does not matter.
- An empty string counts as a palindrome.
isPalindrome(text: string) → bool
C++ needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
bool isPalindrome(std::string text) {
}Worked examples
| Call | Result |
|---|---|
isPalindrome(std::string("")) | true |
isPalindrome(std::string("racecar")) | true |
isPalindrome(std::string("A man, a plan, a canal: Panama")) | true |
isPalindrome(std::string("hello")) | false |
Hint
Walk one index from each end, skipping anything that is not alphanumeric.
Reference solution in C++
bool isPalindrome(std::string text) {
string s;
for (char c : text) {
if (isalnum(static_cast<unsigned char>(c))) s += tolower(static_cast<unsigned char>(c));
}
for (int i = 0, j = (int) s.size() - 1; i < j; i++, j--) {
if (s[i] != s[j]) return false;
}
return true;
}