## Key Concepts

Review core concepts you need to learn to master this subject

### Call Stack Construction in While Loop

A call stack with execution contexts can be constructed using a `while` loop, a `list` to represent the call stack and a `dictionary` to represent the execution contexts. This is useful to mimic the role of a call stack inside a recursive function.

Recursion: Python
Lesson 1 of 2
1. 1
The best way to understand recursion is with lots of practice! At first, this method of solving a problem can seem unfamiliar but by the end of this lesson, we’ll have implemented a variety of algo…
2. 2
In the previous exercise, we used an iterative function to implement how a call stack accumulates execution contexts during recursive function calls. We’ll now address the conclusion of this funct…
3. 3
Now that we’ve built a mental model for how recursion is handled by Python, let’s implement the same function and make it truly recursive. To recap: We want a function that takes an integer as an …
4. 4
Excellent job writing your first recursive function. Our next task may seem familiar so there won’t be as much guidance. We’d like a function factorial that, given a positive integer as input, re…
5. 5
The previous exercise ended with a stack overflow, which is a reminder that recursion has costs that iteration doesn’t. We saw in the first exercise that **every recursive call spends time on th…
6. 6
Let’s use recursion to solve another problem involving lists: flatten(). We want to write a function that removes nested lists within a list but keeps the values contained. nested_planets = […
7. 7
So far our recursive functions have all included a single recursive call within the function definition. Let’s explore a problem which pushes us to use multiple recursive calls within the fun…
8. 8
Data structures can also be recursive. Trees are a recursive data structure because their definition is self-referential. A tree is a data structure which contains a piece of data **and reference…

## How you'll master it

Stress-test your knowledge with quizzes that help commit syntax to memory