Scala algorithm: Reverse bits of an integer
Reverse the bits of an integer, eg 2 becomes 1073741824 as 2 is 0b[30 times of 0-bit]10, so 2 reversed is 0b01[30 times of 0-bit].
Test cases in Scala
Algorithm in Scala
15 lines of Scala (compatible versions 2.13 & 3.0), showing how concise Scala can be!
We take the approach of taking bit-by-bit from the end and using a left binary shift to move that bit to the left side at every iteration.
Note that there is a more efficient implementation that is O(1), but we would be copy-pasting a standard Java algorithm at this point; see
java.lang.Integer.reverse. (this is © from www.scala-algorithms.com)
Scala concepts & Hints
Def Inside Def
A great aspect of Scala is being able to declare functions inside functions, making it possible to reduce repetition.
It is also frequently used in combination with Tail Recursion.
Stack safety is present where a function cannot crash due to overflowing the limit of number of recursive calls.
This function will work for n = 5, but will not work for n = 2000 (crash with java.lang.StackOverflowError) - however there is a way to fix it :-)
In Scala Algorithms, we try to write the algorithms in a stack-safe way, where possible, so that when you use the algorithms, they will not crash on large inputs. However, stack-safe implementations are often more complex, and in some cases, overly complex, for the task at hand.
In Scala, tail recursion enables you to rewrite a mutable structure such as a while-loop, into an immutable algorithm.