Practice problems

Project Euler and 99 Scala Problems or 99 Python Problems contain collections of small coding problems suitable for functional programming - many of them are also good exercises for nuts-flow.

99 Problems

A few 99 Scala Problems with solutions using nuts-flow:

>>> from nutsflow import *
>>> from nutsflow import _

P01 : Find the last element of a list.

>>> [1, 1, 2, 3, 5, 8] >> Tail(1)
[8]

P02 : Find the last but one element of a list.

>>> [1, 1, 2, 3, 5, 8] >> Tail(2) >> Head(1)
[5]

P03 : Find the Kth element of a list.

>>> [1, 1, 2, 3, 5, 8] >> Nth(2)
2

>>> [1, 1, 2, 3, 5, 8] >> Drop(2) >> Head(1)
[2]

P04 : Find the number of elements of a list.

>>> [1, 1, 2, 3, 5, 8] >> Count()
6

P14 : Duplicate the elements of a list.

>>> Range(5) >> Clone(2) >> Collect()
[0, 0, 1, 1, 2, 2, 3, 3, 4, 4]

P15 : Duplicate the elements of a list a given number of times.

>>> Range(5) >> Clone(n) >> Collect()
[0, 0, 1, 1, 2, 2, 3, 3, 4, 4]

P16 : Drop every Nth element from a list.

>>> n==3
>>> lst = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k']
>>> lst >> Chunk(n, list) >> Map(Take(n-1)) >> Flatten() >> Collect()
['a', 'b', 'd', 'e', 'g', 'h', 'j', 'k']

Euler

Some Project Euler with solutions using nuts-flow.

P1: Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

>>> IsMultiple = nut_filter(lambda x: x % 3 == 0 or x % 5 == 0)
>>> Range(1, 1000) >> IsMultiple() >> Sum()
233168

P2: Even Fibonacci numbers

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

>>> @nut_source
... def Fib():
...     a, b =  1, 1
...     while True:
...         a, b = b, a + b
...         yield a
>>> IsEven = nut_filter(lambda x: x%2 == 0)
>>> Fib() >> TakeWhile(_ < 4000000) >> IsEven() >> Sum()
4613732

P4: Largest palindrome product

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

>>> n1, n2  = 100, 1000
>>> IsPalindrom = nut_filter(lambda p: p == p[::-1])
>>> BuildString = nut_function(lambda (a, b): str(a * b))
>>> product = Product(Range(n1, n2), repeat=2)
>>> product >> BuildString() >> IsPalindrom() >> Max(int)
'906609'

P6: Sum square difference

The sum of the squares of the first ten natural numbers is,

1^2 + 2^2 + … + 10^2 = 385

The square of the sum of the first ten natural numbers is,

(1 + 2 + … + 10)^2 = 55^2 = 3025

Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 − 385 = 2640.

Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.

>>> sum_sqr = Range(1, 11) >> Square() >> Sum()
>>> sqr_sum = (Range(1, 11) >> Sum())**2
>>> sqr_sum - sum_sqr
2640