# JavaScript Katas: Find Odd Digits

## Intro π

Problem solving is an important skill, for your career and your life in general.

That's why I take interesting katas of all levels, customize them and explain how to solve them.

## Understanding the Exerciseβ

First, we need to understand the exercise! If you don't understand it, you can't solve it!.

My personal method:

- Input: What do I put in?
- Output: What do I want to get out?

### Today's exercise

Today, another `7 kyu`

kata,
meaning we slightly increase the difficulty.

Source: Codewars

Write a function `findOddDigits`

, that accepts two parameter: `n`

a number and `k`

a number.

Given `n`

, e.g. `123456789111`

, and `k`

, e.g. `5`

, return the first `k`

odd digits in `n`

, e.g. `13579`

.

In the following cases the function should return `0`

:

- there are no odd digits in
`n`

; `k`

is bigger than`n`

;`k`

is`0`

;`k`

is bigger than the number of odd digits in`n`

.

Input: two numbers.

Output: one number.

## Thinking about the Solution π

I think I understand the exercise (= what I put into the function and what I want to get out of it).

Now, I need the specific steps to get from input to output.

I try to do this in small baby steps:

- Find all odd digits
- Find the first
`k`

digits - Handle all edge cases
- Return the number

Example:

- Input:
`123456789111, 5`

- Find all odd digits:
`13579111`

- Find the first
`k`

(=`5`

) digits:`13579`

- Return the number:
`13579`

- Output:
`13579`

β

## Implementation (Explicit) β

```
function findOddDigits(n, k) {
// k = 0;
// k is bigger than a number of digits in n;
if (k === 0 || k > n) return 0;
// find all odd digits
const str = String(n);
const split = str.split("");
const odds = split.filter((num) => num % 2);
// there are no odd digits in a number n;
// k is bigger than a number of odd digits in n.
if (!odds.length || k > odds.length) return 0;
// find the first `k` digits
const joined = odds.join("");
const sliced = joined.slice(0, k);
// return the number
return Number(sliced);
}
```

### Result

```
console.log(findOddDigits(123456789111, 5));
// 13579 β
console.log(findOddDigits(0, 100));
// 0 β
```

## Implementation (Implicit) β

```
function findOddDigits(n, k) {
// find all odd digits
const odds = String(n)
.split("")
.filter((num) => num % 2);
// handle all edge cases
if (k === 0 || k > n || !odds.length || k > odds.length) return 0;
// find the first `k` digits and return them as a number
return Number(odds.join("").slice(0, k));
}
```

### Result

```
console.log(findOddDigits(123456789111, 5));
// 13579 β
console.log(findOddDigits(0, 100));
// 0 β
```

## Playground β½

You can play around with the code here

## Next Part β‘οΈ

Great work!

We learned how to use `String`

, `Number`

, `split`

, `join`

, `filter`

, `slice`

.

I hope you can use your new learnings to solve problems more easily!

Next time, we'll solve another interesting kata. Stay tuned!

If I should solve a specific kata, shoot me a message here.

If you want to read my latest stuff, get in touch with me!

## Further Reading π

## Questions β

- How often do you do katas?
- Which implementation do you like more? Why?
- Any alternative solution?