Scala exercises

A small collection of interesting Scala exercises I found on a web.

Most solutions are test-driven developed.

Testing

The project uses Simple Build Tool (SBT). To execute the tests simply do:

$ sbt test

Exercises

1. Pascal's triangle

The figure below is to be known as a Pascal's Triangle (each value is calculated as a sum of two values immediately above it):

   1
  1 1
 1 2 1
1 3 3 1

Write a function that will recursively calculate the value at the given position (row and column, zero-based).

def pascal(row: Int, column: Int): Int

Example:

pascal(0, 0) = 1
pascal(2, 1) = 2
pascal(3, 2) = 3

2. Fibonacci sequence sum

A fibonacci sequence is a sequence of numbers in which every number is the sum of two previous numbers, like that:

1 1 2 3 5 8 13 21 34 ...

Write a function that will calculate the sum of first n elements.

def fibonacciSum(n: Int): Int

Example:

fibonacciSum(0) = 0
fibonacciSum(1) = 1
fibonacciSum(3) = 4
fibonacciSum(7) = 33

3. Reverse Polish notation

A Reverse Polish notation is a mathematical notation in which every operator follows all of its operands. For example 2 + 2 would be translated to 2 2 +, and ( 2 + 3 ) * 5 would become 2 3 + 5 *.

Write a function that will evaluate an expression in Reverse Polish notation.

def rpn(expr: String): Int

Example:

rpn("2 2 +") = 4
rpn("2 3 + 5 *") = 25

4. Parentheses balancing

Write a recursive function that check whether parentheses are balanced in given sentence.

def isBalanced(sentence: String): Boolean

Example:

isBalanced("(this is balanced)") = true
isBalanced("(oh, this (is) balanced (too))") = true
isBalanced("(this is (not balanced)") = false
isBalanced(")()()()(") = false