https://leetcode.com/problems/subtree-of-another-tree/
Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considered as a subtree of itself.
Example 1:
Given tree s:
3
/ \
4 5
/ \
1 2
Given tree t:
4 / \ 1 2
Return true, because t has the same structure and node values with a subtree of s.
