Given a binary tree, find its maximum depth.
A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
Example 1:
Input:
root --> 1
/ \
3 2
/
4
Output: 3
Explanation:
Maximum depth is between nodes 1 and 4, which is 3.
Example 2:
Input:
root --> 10
/ \
20 30
\ \
40 60
/
2
Output: 4
Explanation:
Maximum depth is between nodes 10 and 2, which is 4
Your Task:
You don't need to read input or print anything. Complete the function maxDepth() which takes the root node as an input parameter and returns the maximum depth.

Expected Time Complexity: O(N)
Expected Auxiliary Space: O(height of the tree)

Constraints:
1 ≤ N ≤ 10^5

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