Palindromes

A palindrome is a word that it is spelled the same forward than backward. For example “ROTOR“

Pseudo-code

  1. If string has no letters or just one letter then it is a palindrome.
  2. Otherwise, compare first and last letters of the string. If they differ it is not a palindrome.
  3. Keep doing the same until you end up with one letter or 0

Implementation

  1. // Returns the first character of the string str
  2. var firstCharacter = function(str) {
  3.     return str.slice(0, 1);
  4. };
  6. // Returns the last character of a string str
  7. var lastCharacter = function(str) {
  8.     return str.slice(-1);
  9. };
  11. // Returns the string that results from removing the first
  12. //  and last characters from str
  13. var middleCharacters = function(str) {
  14.     return str.slice(1, -1);
  15. };
  17. var isPalindrome = function(str) {
  18.     // base case #1
  19.     if (str.length <= 1) {
  20.         return true; 
  21.     }
  22.     // base case #2
  23.     if (firstCharacter(str) !== lastCharacter(str)) { 
  24.         return false; 
  25.     }
  26.     // recursive case
  27.     return (firstCharacter(str) === lastCharacter(str)) && isPalindrome(middleCharacters(str));
  28. };
  30. var checkPalindrome = function(str) {
  31.     println("Is this word a palindrome? " + str);
  32.     println(isPalindrome(str));
  33. };
  35. checkPalindrome("a");
  36. Program.assertEqual(isPalindrome("a"), true);
  37. checkPalindrome("motor");
  38. Program.assertEqual(isPalindrome("motor"), false);
  39. checkPalindrome("rotor");
  40. Program.assertEqual(isPalindrome("rotor"), true);