# JavaScript Coding Challenge: "Birthday Cake Candles"

A couple of days ago I received and email from HackerRank. They invited me to solve one of their challenges so... That's what we're going to do now!

You are in charge of the cake for your niece's birthday and have decided the cake will have one candle for each year of her total age. When she blows out the candles, she’ll only be able to blow out the tallest ones. Your task is to find out how many candles she can successfully blow out.

For example, if your niece is turning 4 years old, and the cake will have 4 candles of height 3, 3, 1, 2, she will be able to blow out 2 candles successfully, since the tallest candles are of height 3 and there are such candles.

## Function description

Create a function: `birthdayCakeCandles`. It must return an integer representing the number of candles she can blow out.

`birthdayCakeCandles` has the following parameter: `arr` - an array of integers representing candle heights.

As you can see it's pretty simple, but if they challenged me... I have to solve it! You can find the challenge on HackerRank.

Note: Before reading forward, I'd recommend that you solve the challenge on your own first. Than you can take a peak 👀 on my solutions.

## First solution - the cleaner way

For this one we're going to do a couple of steps:

1. create a variable which will store the highest candle height. Let's call this variable: `max`
2. (a) loop over the array and (b) increase a `counter` everytime the current `item` is equal to `max`
3. if the `item` is higher than `max`, reset the `counter` and also set `max` to be equal to the `item`
4. at the end, return the `counter`

(`item` is the current candle height from the given `arr`)

``````function birthdayCakeCandles(arr) {
// Step 1
let max = 0;
let counter = 0;

// Step 2 (a)
arr.forEach(item => {
// Step 3
if (item > max) {
// Step 4
max = item;
counter = 1;
// Step 2 (b)
} else if (item === max) {
counter++;
}
});

return counter;
}`````` ## Second solution - the clever but not optimal way

We could also use some 'tricks' to make it easier to understand the code, without having to use both `if` and `else if` statements.

This time let's do the following:

1. use `Math.max` + the `array spread` operator to get the maximum value from the array
2. use the array's `filter` method to return an array with only the `max` values
3. return the length of this `filter`ed array
``````function birthdayCakeCandles(arr) {
let max = Math.max(...arr);
return arr.filter(item => item === max).length;
}``````

It's not the optimal way because are looping twice over the array (int the `Max.max` and the `filter` methods).

## Third solution - the one-liner

(Or the worst but most satisfying way ❤️)

You might know (or if you don't, ask my friend: jenovs) that I like the `reduce` function so everytime I can, I love using it, including this time. 😆

So... for this one, we're going to use a `ternary` operator twice because one `ternary` operator can only handle 2 cases at a time. Plug another one in and you can have 3 cases: 👍

1. `item` > `max`
2. `item` = `max`
3. `item` < `max`

Also, the default value of the `acc` (accumulator) would be an `object` where we're going to save the two values we need: `max` and `counter`.

Other than that we just have to use the 'logic' from the First solution - sort of... • If the `max` is less than the `item` we save it and reset the `counter`.
• Else if the `item` is equal to the `max` we increase the counter and we spread the rest of the object (although we only have one prop and we don't have to use the `spread` operator. We could just re set the `max` again, but... it's nice to see the three dots syntax 😎 ).
• Else, just return the `object`

And at the end, we return the `counter` prop of the returning `object`.

``````const birthdayCakeCandles = arr =>
arr.reduce(
(acc, item) =>
acc.max < item
? { max: item, counter: 1 }
: acc.max === item
? { ...acc, counter: ++acc.counter }
: acc,
{ max: 0, counter: 0 }
).counter;``````

## Conclusion

That's all we have for now... a simple problem with a simple solution. 😉

As always, I had fun coming up with all these solutions. Which one did you like the most?

Maybe you found another solution... I'd like to see it so let me know. You can brag about it! 😆

Tagged with math, max, es6