Palindrome.cpp

/*
isPalindrome Algorithm in C++

A phrase is a palindrome if, after converting all uppercase letters into
lowercase letters and removing all non-alphanumeric characters, it reads the
same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.
*/
#include <iostream>

#include <string>

using namespace std;

bool isPalindrome(string s) {
  // Step 1: Convert all characters to lowercase
  for (char &c : s) {
    c = std::tolower(c);
  }

  // Step 2: Remove non-alphanumeric characters
  std::string alphanumericStr;
  for (char c : s) {
    if (std::isalnum(c)) {
      alphanumericStr.push_back(c);
    }
  }

  // Step 3: Check if the resulting string is a palindrome
  int left = 0;
  int right = alphanumericStr.length() - 1;

  while (left < right) {
    if (alphanumericStr[left] != alphanumericStr[right]) {
      return false;
    }
    left++;
    right--;
  }
  return true;
}

int main() {
  std::string input;
  std::cout << "Enter a string: ";
  std::getline(std::cin, input);

  if (isPalindrome(input)) {
    std::cout << "The string is a palindrome." << std::endl;
  } else {
    std::cout << "The string is not a palindrome." << std::endl;
  }
  return 0;
}