1372. Longest ZigZag Path in a Binary Tree (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def longestZigZag(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        self.result = 0
        def dfs(node, fromLeft, length):
            if node:
                if fromLeft:
                    dfs(node.left, True, 1)
                    dfs(node.right, False, length + 1)
                else:
                    dfs(node.left, True, length + 1)
                    dfs(node.right, False, 1)
                self.result = max(length, self.result)
        dfs(root.left, True, 1)
        dfs(root.right, False, 1)
        return self.result