Update computer-science/algorithms/palindromes.md

computer-science/algorithms/palindromes.md

@@ -1,2 +1,55 @@
 # 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
+
+```javascript
+// Returns the first character of the string str
+var firstCharacter = function(str) {
+    return str.slice(0, 1);
+};
+
+// Returns the last character of a string str
+var lastCharacter = function(str) {
+    return str.slice(-1);
+};
+
+// Returns the string that results from removing the first
+//  and last characters from str
+var middleCharacters = function(str) {
+    return str.slice(1, -1);
+};
+
+var isPalindrome = function(str) {
+    // base case #1
+    if (str.length <= 1) {
+        return true; 
+    }
+    // base case #2
+    if (firstCharacter(str) !== lastCharacter(str)) { 
+        return false; 
+    }
+    // recursive case
+    return (firstCharacter(str) === lastCharacter(str)) && isPalindrome(middleCharacters(str));
+};
+
+var checkPalindrome = function(str) {
+    println("Is this word a palindrome? " + str);
+    println(isPalindrome(str));
+};
+
+checkPalindrome("a");
+Program.assertEqual(isPalindrome("a"), true);
+checkPalindrome("motor");
+Program.assertEqual(isPalindrome("motor"), false);
+checkPalindrome("rotor");
+Program.assertEqual(isPalindrome("rotor"), true);
+
+```