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Daily Challenge #189 - Convert Number into Reversed Array

dev.to staff on February 16, 2020

Setup Write a function that takes a random number as input and converts it into an array with the digits of that number appearing in rev...

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Alvaro Montoro • Feb 16 '20

A one liner in JavaScript:

const convertNtA = num => Number(num) && num >= 0 && (num+"").split("").reverse() || null;

It checks if it's a positive number, then turns it into a string, separate the characters and reverse them. If the parameter is not valid, it returns null.

Alvaro Montoro • Feb 16 '20

This will process numbers that some people may not consider valid as they contain characters different than digits (e.g. 12e10).

Also having those && combined with || like that is not pretty... don't do it :P

Hao • Feb 17 '20

The result should be an array of numbers but this yields an array of strings.
Maybe consider adding .map(Number) after .reverse()?

Amin • Feb 16 '20 • Edited

JavaScript

Assuming the input should be a positive integer as in the test cases.

Using modulo and division should make it an O(n) solution, n being the number of digits in the number.

We could also have used the toString method from the Number.prototype and then use a spread operator into an array, and then use the Array.prototype.reverse method to reverse each one of its digits, but that would have made the function run in O(n³) space I believe.

"use strict";

/**
 * @function
 * @name convertNtA
 * @summary Convert a number into an array of each digits reversed.
 * @param {number} number The number to convert.
 * @throws {Error} If the function is not called with exactly one argument.
 * @throws {TypeError} If the first argument is not a number
 * @throws {TypeError} If the first argument is not a number.
 * @throws {TypeError} If the first argument is lower than zero.
 * @return {number[]} The converted number.
 * @example
 * convertNtA(348597); // [7, 9, 5, 8, 4, 3]
 * convertNtA(6581554); // [4, 5, 5, 1, 8, 5, 6]
 * convertNtA(123456); // [6, 5, 4, 3, 2, 1]
 * convertNtA(987123); // [3, 2, 1, 7, 8, 9]
 *
 */
function convertNtA(number) {
    if (arguments.length !== 1) {
        throw new Error("Expected exactly one argument");
    }

    if (typeof number !== "number") {
        throw new TypeError("Expected first argument to be a number.");
    }

    if (number !== (number | 0)) {
        throw new TypeError("Expected first argument to be an integer.");
    }

    if (number < 0) {
        throw new RangeError("Expected first argument to be greater or equal to zero.");
    }

    const output = [];

    while (number !== 0) {
        const lastDigit = number % 10;

        output.push(lastDigit);

        number = number / 10 | 0;
    }

    return output;
}

Vidit Sarkar • Feb 16 '20 • Edited

C++

vector<int> convertNtA(long number){
    vector<int> numDigits;
    if(number == 0) // if number is zero then return vector with only 0
        return vector<int>({0});

    while(number > 0){
        numDigits.push_back(number%10);
        number /= 10;
    }
    return numDigits;
}

Python one liner

def convertNtA(number):
    return list(map(int,str(number)[::-1]))
print(convertNtA(123456))

convertNtA = lambda number : list(map(int,str(number)[::-1]))
print(convertNtA(123456))

Andrei McMillan • Feb 16 '20

python

def convert_n_t_a(in_str):
    arr = list(in_str)
    arr.reverse()
    return arr

# --------------


print convert_n_t_a('348597')
print convert_n_t_a('6581554')
print convert_n_t_a('123456')
print convert_n_t_a('987123')

Nijeesh Joshy • Feb 26 '20

dude, I don't think the input to the function is a string.

Mihail Malo • Mar 3 '20

Whoops, looks like someone didn't specify the base of the number :o
How naughty!

function convertNtA(num, base = 10) {
  const len = Math.ceil(Math.log(num) / Math.log(base)),
    arr = Array(len)
  for (let i = 0; i < len; i++) {
    arr[i] = num % base
    num = (num / base) | 0
  }
  return arr
}
convertNtA(348597)
convertNtA(0x348597, 16)

Nijeesh Joshy • Feb 26 '20 • Edited

ruby


def convert_nt_a number
  number
    .to_s
    .split('')
    .reverse
    .map { |num| num.to_i }
end


# TESTS

require "test/unit"

class ConvertNtATest < Test::Unit::TestCase
  def test_convert_nt_a
    assert_equal [7,9,5,8,4,3],  convert_nt_a(348597)
    assert_equal [4, 5, 5, 1, 8, 5, 6],  convert_nt_a(6581554)
    assert_equal [6, 5, 4, 3, 2, 1],  convert_nt_a(123456)
    assert_equal [3, 2, 1, 7, 8, 9], convert_nt_a(987123)
  end
end

#1 tests, 4 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications

Craig McIlwrath • Feb 16 '20

Haskell:

convertNtA :: (Integral a) -> a -> [a]
convertNtA 0 = [] 
convertNtA n = n `mod` 10 : convertNtA (n `div` 10)

SavagePixie • Feb 16 '20

Elixir one-liner:

def to_list_reverse(n), do: Integer.digits(n) |> Enum.reverse

Lamonte • Feb 16 '20

dart

List<int> reverseToArray(int number) {
  return number.toString().split("").reversed.map(int.parse).toList();
}

Jay • Feb 17 '20

Rust one liner:

fn convertNtA(num: i32) -> Vec<u32> {
    num.to_string()
        .chars()
        .map(|c| c.to_digit(10).unwrap())
        .rev()
        .collect()
}

Bk Aguilar • Feb 25 '20 • Edited

In JavaScript


const converseNumber = n => Array.from(n.toString()).reverse().map(Number);