We mentioned `.heapify_down()`

is a lot like `.heapify_up()`

. We’ll track an offending element in the heap, and keep swapping it with another element until we’ve restored the heap properties.

The wrinkle is `.heapify_down()`

gives us **another option** for which element to swap. In `.heapify_up()`

, we were always comparing our element with its parent. In `.heapify_down()`

, we have potentially two options: the left child and the right child.

Which should we choose? We’ll use an example to think it through. Imagine we have a heap with four elements:

```
print(heap.heap_list)
# [None, 21, 36, 58, 42]
heap.retrieve_min()
# 21
# [None, 42, 36, 58]
# Should we swap with 36 or 58?
```

We want to swap with the **smaller** of the two children, otherwise, we wouldn’t maintain our heap properties!

Let’s write a helper method to determine the smallest child element for a given index. We’ll make heavy use of our other helper methods: `.left_child_idx()`

and `.right_child_idx()`

.

`.get_smaller_child_idx()`

will have the following structure:

```
# check if we have a right child
# if we don't, return the left child index
# if we do...
# return the index of the smaller child
```

### Instructions

**1.**

Define `.get_smaller_child_idx()`

, it will take `self`

and `idx`

as arguments.

Check if we have a right child for this index. We don’t if the right child index is greater than our internal count.

If we don’t, print “There is only a left child” and return the left child index.

**2.**

**If we do have a right child**, we need to make a comparison to see which is smaller.

Declare `left_child`

and `right_child`

as variables and assign them to the appropriate elements from the internal list.

You can do this by using helper methods `.left_child_idx()`

and `.right_child_idx()`

to access elements in `self.heap_list`

.

**3.**

Make another conditional for the comparison between `left_child`

and `right_child`

.

If the left child is smaller, print a message saying so and return the **index** of the left child.

Else, do the same but for the right child.

**4.**

Tab over to **script.py** and test out this new method by replacing `None`

with the correct index value.