0104 Maximum Depth of Binary Tree

Question

My Solution:

Recursive DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    
    
    public int maxDepth(TreeNode root) {
        if(root == null) 
            return 0;
        int leftMax = maxDepth(root.left);
        int rightMax = maxDepth(root.right);
        
        return Math.max(leftMax, rightMax) + 1;
    }
}

Python

Bread First Search

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if not root:
            return 0
        
        level = 0
        q = deque([root])
        while q: # while q is not empty
            for i in range(len(q)):
                node = q.popleft()
                if node.left: # node have left child
                    q.append(node.left)
                if node.right:
                    q.append(node.right)
            
            level += 1
        
        return level

Iterative DFS

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        stack = [[root, 1]]
        res = 0

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

            if node: # if node is not None 
                res = max(res, depth)
                stack.append([node.left, depth + 1])
                stack.append([node.right, depth + 1])
            
        return res