Leetcode 1474 Solution

This article provides solution to leetcode question 1474 (longest-zigzag-path-in-a-binary-tree)
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https://leetcode.com/problems/longest-zigzag-path-in-a-binary-tree

Solution

# 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 longestZigZag(self, root: Optional[TreeNode]) -> int:
        ans = 0

        def dfs(node):
            nonlocal ans

            if not node:
                return -1, -1

            left_max = dfs(node.left)[1] + 1
            right_max = dfs(node.right)[0] + 1

            ans = max(ans, left_max, right_max)
            return left_max, right_max

        dfs(root)

        return ans