All Root-to-Leaf Paths

Return every root-to-leaf path as a string like "1->2->5". List the paths from left to right: all the paths through the left subtree come before the paths through the right subtree.

The tests write a tree as a level-order list (row by row, left to right) with None for a missing child: [3, 9, 20, None, None, 15, 7] is a root 3 with children 9 and 20, where 20 has children 15 and 7.

For [1, 2, 3, None, 5] the answer is ["1->2->5", "1->3"].

Examples

Example 1

Input:

root_to_leaf_paths(root)  # root = [1, 2, 3, None, 5]

Output:

['1->2->5', '1->3']

Example 2

Input:

root_to_leaf_paths(root)  # root = [1]

Output:

['1']

Constraints

• 0 <= number of nodes <= 20000
• The tree is not deeper than 800 levels.
• -100 <= val <= 100