miku86

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# JavaScript Katas: Find Odd Digits

## Intro 🌐

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 Exercise❗

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

My personal method:

1. Input: What do I put in?
2. 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 💭

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:

1. Find all odd digits
2. Find the first `k` digits
3. Handle all edge cases
4. 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`

## Implementation (Explicit) ⛑

``````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 ✅

console.log(findOddDigits(0, 100));
// 0 ✅
``````

## Implementation (Implicit) ⛑

``````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 ✅

console.log(findOddDigits(0, 100));
// 0 ✅
``````

## Playground ⚽

You can play around with the code here

## Next Part ➡️

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!

## Questions ❔

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

let stringN = numbers.toString()
let countODD = []
let result = ""

``````if (k > numbers || k === 0) {
result = 0
} else {
for (const number of stringN) {
if (number % 2 !== 0) {
countODD.push(number)
}
}
for (let i = 0; i < k; i++) {
result += countODD[i]
if (countODD[i] === undefined){
result = 0
}
}
}
console.log(Number(result))
``````

JP Antunes

And now in one single (almost readable) line!

``````const odds = (n, k) => n > Math.max(0, k) ? Number([...`\${n}`].filter(num => num % 2).join('').slice(0, k)) : 0
``````