[Leetcode]Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

这题要返回树的最大深度~  递归解法很简单

class Solution:
    # @param root, a tree node
    # @return an integer
    def maxDepth(self, root):
        if root is None: return 0
        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1

还有一种非递归解法，采用层序遍历

class Solution:
    # @param root, a tree node
    # @return an integer
    def maxDepth(self, root):
        if root is None: return 0
        depth = 1
        queue = [root, None]
        while len(queue) > 1:
            node = queue.pop(0)
            if node is None:
                depth += 1
                queue.append(None)
                continue
            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)
        return depth