# Daily Challenge #189 - Convert Number into Reversed Array

### 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 reverse order.

### Example

`convertNtA(348597)` => `[7,9,5,8,4,3]`

### Tests

`convertNtA(6581554)`
`convertNtA(123456)`
`convertNtA(987123)`

Good luck!~

This challenge comes from emporio on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions! Alvaro Montoro

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

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

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

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

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

`````` SavagePixie

Elixir one-liner:

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

Rust one liner:

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