LeetCode-in-Java
1372. Longest ZigZag Path in a Binary Tree
Medium
You are given the root of a binary tree.
A ZigZag path for a binary tree is defined as follow:
- Choose any node in the binary tree and a direction (right or left).
- If the current direction is right, move to the right child of the current node; otherwise, move to the left child.
- Change the direction from right to left or from left to right.
- 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:
Input: root = [1,null,1,1,1,null,null,1,1,null,1,null,null,null,1,null,1]
Output: 3
Explanation: Longest ZigZag path in blue nodes (right -> left -> right).
Example 2:
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:
- The number of nodes in the tree is in the range
[1, 5 * 104]. 1 <= Node.val <= 100
Solution
import com_github_leetcode.TreeNode;
/*
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
public class Solution {
private int maxLength = 0;
public int longestZigZag(TreeNode root) {
dfs(root, true);
return maxLength;
}
private int dfs(TreeNode root, boolean isLeft) {
if (root == null) {
return 0;
}
int left = dfs(root.left, false);
int right = dfs(root.right, true);
maxLength = Math.max(maxLength, left);
maxLength = Math.max(maxLength, right);
return 1 + (isLeft ? left : right);
}
}