LeetCode 257. Binary Tree Paths

257. Binary Tree Paths
Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

1
/ \
2 3
\
5
All root-to-leaf paths are:

[“1->2->5”, “1->3”]
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.