Add Happy Number solution

Author: marttp

kotlin/Fast and Slow Pointers/HappyNumber.kt

@@ -0,0 +1,30 @@
+fun happyNumber(n: Int): Boolean {
+    var slow = n
+    var fast = n
+    while (true) {
+        slow = getNextNum(slow)
+        fast = getNextNum(getNextNum(fast))
+        if (fast == 1) {
+            return true
+        // If the fast and slow pointers meet, a cycle is detected. 
+        // Hence, 'n' is not a happy number.
+        } else if (fast == slow) {
+            return false
+        }
+    }
+}
+
+fun getNextNum(x: Int): Int {
+    var nextNum = 0
+    var num = x
+    while (num > 0) {
+        // Extract the last digit of 'x'.
+        val digit = num % 10
+        // Truncate (remove) the last digit from 'x' using floor 
+        // division.
+        num /= 10
+        // Add the square of the extracted digit to the sum.
+        nextNum += digit * digit
+    }
+    return nextNum
+}