1372. Longest ZigZag Path in a Binary Tree (ILeetcode)

/**
 * 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;
 *     }
 * }
 */


 class Solution {
    private int ans = 0;
    private static final String LEFT = "left";
    private static final String RIGHT = "right";
     
    void helper(TreeNode root, int dis, String direction) {
        if (root == null) return;
        ans = Math.max(ans, dis);
        if (direction == LEFT) {
            helper(root.left, dis + 1, RIGHT);
            helper(root.right, 1, LEFT);
        } else {
            helper(root.right, dis + 1, LEFT);
            helper(root.left, 1, RIGHT);
        }
    }

    public int longestZigZag(TreeNode root) {
        helper(root, 0, LEFT);
        helper(root, 0, RIGHT);
        return ans;
    }
}