97. Maximum Depth of Binary Tree

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本文介绍了一种求解二叉树最大深度的算法，并提供了递归和非递归两种实现方式。通过实例演示了如何计算从根节点到最远叶节点的最长路径上的节点数。

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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.

Example
Given a binary tree as follow:

The maximum depth is 3.

Python:

    """
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
    self.val = val
    self.left, self.right = None, None
"""
class Solution:
"""
@param root: The root of binary tree.
@return: An integer
""" 
'''
# divide and conquer
def maxDepth(self, root):
    if root is None:
        return 0
    left = self.maxDepth(root.left)
    right = self.maxDepth(root.right)
    return 1 + max(left, right)
'''

'''
# non recursion
def maxDepth(self, root):
    if root is None:
        return 0
    stack = [root]
    depth = 0
    while stack:
        next = []
        depth += 1
        for item in stack:
            if item.left:
                next.append(item.left)
            if item.right:
                next.append(item.right)
        stack = next
    return depth
'''        

result = float('-inf')

def maxDepth(self, root):
    if root is None:
        return 0
    self.helper(root, 1)
    return self.result

def helper(self, root, depth):
    if root.left is None and root.right is None:
        self.result = max(self.result, depth)
    if root.left:
        self.helper(root.left, depth + 1)
    if root.right:
        self.helper(root.right, depth + 1)