104_maximumDepthOfBinaryTree.py

## Recursive 
#class Solution:
#    def maxDepth(self, root: Optional[TreeNode]) -> int:
#        if not root:
#            return 0
#
#        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))
        
## BFS
#class Solution:
#    def maxDepth(self, root: Optional[TreeNode]) -> int:
#        q = deque()
#        if root:
#            q.append(root)
#        level = 0
#        while q:
#            for i in range(len(q)):
#                node = q.popleft()
#                if node.left:
#                    q.append(node.left)
#                if node.right:
#                    q.append(node.right)
#            level += 1
#        return level

## DFS
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        stack = [[root, 1]]
        res = 0

        while stack:
            node, depth = stack.pop()

            if node:
                res = max(res, depth)
                stack.append([node.left, depth + 1])
                stack.append([node.right, depth + 1])
        return res