/* The following code was written in response to this question: https://www.sololearn.com/Discuss/297494/how-to-extract-palindrome-words-from-sentence The "extract_palindromes" function takes a string and returns a collection of substrings, which contains each word in the given string that is a palindrome. Punctuation is ignored, so words containing apostrophes for example will be treated as separate words (not that it matters; there's no palindrome in the English language containing an apostrophe). */ #include #include #include std::vector extract_palindromes(const std::string& input) { std::vector palindromes; // The outer loop finds the starting boundary of a word. for (size_t begin = 0; begin < input.length(); ++begin) { // Check to see if the next character is part of a word. if (isalnum(input[begin])) { // If we've found a word, find the ending boundary of that word. size_t end = begin + 1; for (; end < input.length() && isalnum(input[end]); ++end); // Now check if the word is a palindrome. for (size_t left = begin, right = end; left < right && tolower(input[left++]) == tolower(input[--right]);) if (left >= right) // If the two boundaries intersect, the word is a palindrome! Add it to our list. palindromes.push_back(input.substr(begin, end - begin)); // Now move our starting boundary to the end of the word, so we can look for the next one. begin = end; } } // Return the resulting collection of palindromes. return palindromes; } int main() { std::vector palindromes = extract_palindromes("Madam, this is a racecar from 2002."); for (size_t i = 0; i < palindromes.size(); ++i) std::cout << palindromes[i] << "\n"; return 0; }