solution2.5.2.8.scala provided (#76)

* solution2.5.2.8.scala provided Signed-off-by: Andreas Roehler <[email protected]> * solution2.5.2.8_stream_iterate.scala provided Signed-off-by: Andreas Roehler <[email protected]> * Use revDigits in isPalindrome Signed-off-by: Andreas Roehler <[email protected]> * Use revDigits in isPalindrome again Signed-off-by: Andreas Roehler <[email protected]> * typo Signed-off-by: Andreas Roehler <[email protected]> --------- Signed-off-by: Andreas Roehler <[email protected]>
winitzki · Dec 1, 2024 · 0ea97f1 · 0ea97f1
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diff --git a/chapter02/worksheets/solution2.5.2.8.scala b/chapter02/worksheets/solution2.5.2.8.scala
@@ -0,0 +1,45 @@
+/** 
+  Exercise 2.5.2.8
+
+  (a) Reverse an integer’s digits (see Example 2.5.1.6) as shown:
+  def revDigits(n: Int): Int = ???
+
+  scala> revDigits(12345)
+  res0: Int = 54321
+
+  (b) A palindrome integer is an integer number n such that revDigits(n) == n.
+
+  Write a predicate function of type Int => Boolean that checks
+  whether a given positive integer is a palindrome.
+  */
+
+def revDigits (n: Int): Int = {
+  n.toString.reverse.toInt
+}
+
+val result = revDigits(12345)
+val expected: Int = 54321
+assert(result == expected) 
+
+def isPalindrome(n: Int): Boolean = {
+  revDigits(n) == n
+}
+
+val iPexpected: Boolean = false
+val iPresult = isPalindrome(123)
+assert(iPresult == iPexpected) 
+
+val iPexpected2: Boolean = true
+val iPresult2 = isPalindrome(123321)
+assert(iPresult2 == iPexpected2) 
+
+// scala> :load solution2.5.2.8.scala
+// :load solution2.5.2.8.scala
+// def revDigits(n: Int): Int
+// val result: Int / 54321
+// val expected: Int = 54321
+// def isPalindrome(n: Int): Boolean
+// val iPexpected: Boolean = false
+// val iPresult: Boolean = false
+// val iPexpected2: Boolean = true
+// val iPresult2: Boolean = true
diff --git a/chapter02/worksheets/solution2.5.2.8_stream_iterate.scala b/chapter02/worksheets/solution2.5.2.8_stream_iterate.scala
@@ -0,0 +1,47 @@
+/** 
+  Exercise 2.5.2.8
+
+  (a) Reverse an integer’s digits (see Example 2.5.1.6) as shown:
+  def revDigits(n: Int): Int = ???
+
+  scala> revDigits(12345)
+  res0: Int = 54321
+
+  (b) A palindrome integer is an integer number n such that revDigits(n) == n.
+
+  Write a predicate function of type Int => Boolean that checks
+  whether a given positive integer is a palindrome.
+  */
+
+def revDigits(n: Int): Int = {
+  Stream.iterate(n)(_ / 10).takeWhile(_ != 0).map(_ % 10).toList.reverse.foldRight(0)(_ + _ * 10)
+}
+
+val result = revDigits(12345)
+val expected: Int = 54321
+assert(result == expected) 
+
+def isPalindrome(n: Int): Boolean = {
+  revDigits(n) == n
+}
+
+val iPexpected: Boolean = false
+val iPresult = isPalindrome(123)
+assert(iPresult == iPexpected) 
+
+val iPexpected2: Boolean = true
+val iPresult2 = isPalindrome(123321)
+assert(iPresult2 == iPexpected2) 
+
+// scala> :load solution2.5.2.8_stream_iterate.scala
+// :load solution2.5.2.8_stream_iterate.scala
+// there was 1 deprecation warning; re-run with -deprecation for details
+// 1 warning found
+// def revDigits(n: Int): Int
+// val result: Int = 54321
+// val expected: Int = 54321
+// def isPalindrome(n: Int): Boolean
+// val iPexpected: Boolean = false
+// val iPresult: Boolean = false
+// val iPexpected2: Boolean = true
+// val iPresult2: Boolean = true