Leaf Nodes Retrieval from Binary Tree

Given a binary tree, implement a function that returns a list of leaf nodes following their appearance from left to right. If leaf nodes are equidistant from the leftmost node, preference is given to the node at a lesser depth.

Input:

Elements in level order form with node values separated by spaces, where a null node is represented by -1.

Output:

A list of all leaf nodes of the binary tree in the order they appear from left to right.

Example:

Input:

1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1

Output:

[7, 5, 6]

Explanation:

The given binary tree is:

• Level 1: Root has node 1.
• Level 2: Node 1 has children 2 and 3.
• Level 3: Node 2 has a left child 4; Node 3 has children 5 and 6.
• Level 4: Node 4 has a right child 7.

The leaf nodes are 7, 5, and 6, appearing left-to-right.

Constraints:

• 0 <= N <= 10⁵
• 0 <= Node value <= 10⁸
• Time limit: 1 second