# Solution Review: Calculating the Size of a Tree

This lesson contains the solution review for the challenge of calculating the size of a binary tree.

## We'll cover the following

In this lesson, we will review a solution to the problem of determining the size of a binary tree.

The “size” of a binary tree is the total number of nodes present in the binary tree. We will explicitly define this quantity in greater detail and cover a strategy for how one may calculate this quantity in the binary tree data structure we have been building in this chapter.

We will discuss an iterative and a recursive approach for solving this challenge.

## Iterative Approach

In the iterative solution, we’ll make use of a stack on which we can push the starting node and increment size by `1`

. Next, we’ll pop elements and push their children on to the stack if they have any. For every push, we’ll increment size by `1`

. When the stack becomes empty, the count for the size will also be final. Have a look at the slides below to check out the algorithm:

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