How to resolve the algorithm Tau number step by step in the Python programming language

Published on 12 May 2024 09:40 PM

How to resolve the algorithm Tau number step by step in the Python programming language

Table of Contents

Problem Statement

A Tau number is a positive integer divisible by the count of its positive divisors.

Show the first   100   Tau numbers. The numbers shall be generated during run-time (i.e. the code may not contain string literals, sets/arrays of integers, or alike).

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Tau number step by step in the Python programming language

The given Python code provides two approaches to finding and printing the first 100 "Tau numbers." Tau numbers are positive integers that are divisible by the count of their positive divisors.

Approach 1: Using a Loop and Assertions

The first part of the code uses a loop and assertions to find Tau numbers:

  • The tau function takes an integer n and calculates the number of positive divisors of n.
  • The is_tau_number function checks if n is a Tau number by determining if n is divisible by the number of its divisors.
  • The code iterates through positive integers until it finds 100 Tau numbers and stores them in the ans list.

Approach 2: Using Generators and Functional Programming

The second part of the code utilizes generators and functional programming techniques:

  • The tauNumbers generator yields Tau numbers indefinitely.
  • The divisors function returns a list of divisors for a given number.
  • The primeFactors function extracts the prime factors of a number.
  • The code uses various helper functions, such as chunksOf, take, and until, to manipulate and format the data.

Main Function:

The main function uses the tauNumbers generator to compute the first 100 Tau numbers and prints them in a formatted manner using chunksOf to group them into columns.

Source code in the python programming language

def tau(n):
    assert(isinstance(n, int) and 0 < n)
    ans, i, j = 0, 1, 1
    while i*i <= n:
        if 0 == n%i:
            ans += 1
            j = n//i
            if j != i:
                ans += 1
        i += 1
    return ans

def is_tau_number(n):
    assert(isinstance(n, int))
    if n <= 0:
        return False
    return 0 == n%tau(n)

if __name__ == "__main__":
    n = 1
    ans = []
    while len(ans) < 100:
        if is_tau_number(n):
            ans.append(n)
        n += 1
    print(ans)


'''Tau numbers'''

from operator import mul
from math import floor, sqrt
from functools import reduce
from itertools import (
    accumulate, chain, count,
    groupby, islice, product
)


# tauNumbers :: Generator [Int]
def tauNumbers():
    '''Positive integers divisible by the
       count of their positive divisors.
    '''
    return (
        n for n in count(1)
        if 0 == n % len(divisors(n))
    )


# ------------------------- TEST -------------------------
# main :: IO ()
def main():
    '''The first hundred Tau numbers.
    '''
    xs = take(100)(
        tauNumbers()
    )
    w = len(str(xs[-1]))
    print('\n'.join([
        ' '.join([
            str(cell).rjust(w, ' ') for cell in row
        ])
        for row in chunksOf(10)(xs)
    ]))


# ----------------------- GENERIC ------------------------

# chunksOf :: Int -> [a] -> [[a]]
def chunksOf(n):
    '''A series of lists of length n, subdividing the
       contents of xs. Where the length of xs is not evenly
       divible, the final list will be shorter than n.
    '''
    def go(xs):
        return (
            xs[i:n + i] for i in range(0, len(xs), n)
        ) if 0 < n else None
    return go


# divisors :: Int -> [Int]
def divisors(n):
    '''The ordered divisors of n.
    '''
    def go(a, x):
        return [a * b for a, b in product(
            a,
            accumulate(chain([1], x), mul)
        )]
    return sorted(
        reduce(go, [
            list(g) for _, g
            in groupby(primeFactors(n))
        ], [1])
    ) if 1 < n else [1]


# primeFactors :: Int -> [Int]
def primeFactors(n):
    '''A list of the prime factors of n.
    '''
    def f(qr):
        r = qr[1]
        return step(r), 1 + r

    def step(x):
        return 1 + (x << 2) - ((x >> 1) << 1)

    def go(x):
        root = floor(sqrt(x))

        def p(qr):
            q = qr[0]
            return root < q or 0 == (x % q)

        q = until(p)(f)(
            (2 if 0 == x % 2 else 3, 1)
        )[0]
        return [x] if q > root else [q] + go(x // q)

    return go(n)


# take :: Int -> [a] -> [a]
# take :: Int -> String -> String
def take(n):
    '''The prefix of xs of length n,
       or xs itself if n > length xs.
    '''
    def go(xs):
        return (
            xs[0:n]
            if isinstance(xs, (list, tuple))
            else list(islice(xs, n))
        )
    return go


# until :: (a -> Bool) -> (a -> a) -> a -> a
def until(p):
    '''The result of repeatedly applying f until p holds.
       The initial seed value is x.
    '''
    def go(f):
        def g(x):
            v = x
            while not p(v):
                v = f(v)
            return v
        return g
    return go


# MAIN ---
if __name__ == '__main__':
    main()


  

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