# leetle

## 34. Binary Tree Inorder Traversal

Write a function `solve` that returns the inorder traversal of a binary tree's nodes' values. The tree is represented as an array of nodes in [level-order traversal](https://en.wikipedia.org/wiki/Tree_traversal#/media/File:Sorted_binary_tree_breadth-first_traversal.svg). None indicates empty nodes.

**Example:** `Input: [1,None,2,3]` `Output: [1,3,2]`

Make sure you `return` your solution, don't print!

```python
# Binary Tree Definition
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def solve(root):
    pass
```