Check whether two binary trees are identical.
Example 1
Input: p = [1,2,3], q = [1,2,3]
Output: True
Explanation: The trees are identical.
Output: True
Explanation: The trees are identical.
Example 2
Input: p = [1,2], q = [1,null,2]
Output: False
Explanation: The trees have different structures.
Output: False
Explanation: The trees have different structures.