{leetcode}/problems/longest-zigzag-path-in-a-binary-tree/[LeetCode - 1372. Longest ZigZag Path in a Binary Tree ^]
You are given the root of a binary tree.
A ZigZag path for a binary tree is defined as follow:
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Choose *any *node in the binary tree and a direction (right or left).
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If the current direction is right, move to the right child of the current node; otherwise, move to the left child.
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Change the direction from right to left or from left to right.
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Repeat the second and third steps until you can’t move in the tree.
Zigzag length is defined as the number of nodes visited - 1. (A single node has a length of 0).
Return the longest ZigZag path contained in that tree.
Example 1: <img alt="" src="https://assets.leetcode.com/uploads/2020/01/22/sample_1_1702.png" style="width: 221px; height: 383px;" />
Input: root = [1,null,1,1,1,null,null,1,1,null,1,null,null,null,1] Output: 3 Explanation: Longest ZigZag path in blue nodes (right -> left -> right).
Example 2: <img alt="" src="https://assets.leetcode.com/uploads/2020/01/22/sample_2_1702.png" style="width: 157px; height: 329px;" />
Input: root = [1,1,1,null,1,null,null,1,1,null,1] Output: 4 Explanation: Longest ZigZag path in blue nodes (left -> right -> left -> right).
Example 3:
Input: root = [1] Output: 0
Constraints:
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The number of nodes in the tree is in the range
[1, 5 * 104]. -
1 ⇐ Node.val ⇐ 100