solution2.5.2.9.scala provided

chapter02/worksheets/solution2.5.2.9.scala

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+/** 
+  Exercise 2.5.2.9
+  Define a function findPalindrome: Long => Long
+  performing the following computation:
+
+  First define f(n) = revDigits(n) + n for a given integer n,
+  where the function revDigits was defined in Exercise 2.5.2.8.
+
+  If f(n) is a palindrome integer, findPalindrome returns that integer.
+
+  Otherwise, it keeps applying the same transformation and computes
+  f(n), f(f(n)), ..., until a palindrome integer is eventually found
+  (this is mathematically guaranteed).
+
+  A sample test:
+  scala> findPalindrome(10101)
+  val res0: Long = 20202
+
+  scala> findPalindrome(123)
+  res0: Long = 444
+
+  scala> findPalindrome(83951)
+  res1: Long = 869363968
+
+ */
+
+def revDigits (n: Long): Long = {
+  n.toString.reverse.toLong
+}
+
+def findPalindrome(n: Long): Long = {
+  val a = n.toString.reverse.toLong + n
+  if (revDigits(a) == a) a
+  else
+    findPalindrome(a)
+}
+
+val result = findPalindrome(10101)
+val expected: Long = 20202
+assert(result == expected)
+
+val result1 =  findPalindrome(123)
+val expected1: Long = 444
+assert(result1 == expected1)
+
+val result2 =   findPalindrome(83951)
+val expected2: Long = 869363968
+assert(result2 == expected2)
+
+// scala> :load solution2.5.2.9.scala
+// :load solution2.5.2.9.scala
+// def revDigits(n: Long): Long
+// def findPalindrome(n: Long): Long
+// val result: Long = 20202
+// val expected: Long = 20202
+// val result1: Long = 444
+// val expected1: Long = 444
+// val result2: Long = 869363968
+// val expected2: Long = 869363968