37. 1372. Longest ZigZag Path in a Binary Tree

/**
 * 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 {
    int maxPath = 0;
    public int longestZigZag(TreeNode root) {
        pathSize(root,0,true); // go to left
        pathSize(root,0,false); //go to right
        return maxPath;
        
    }

    private void pathSize(TreeNode root, int step,boolean goLeft){
        if(root==null)return;

        maxPath = Math.max(maxPath,step);

        if(goLeft){
            pathSize(root.left,step+1,false);//now go to right
            pathSize(root.right,1,true); //now go to left, currently traverse right
        }else{
            pathSize(root.right,step+1,true);//go to left
            pathSize(root.left,1,false);//got to right
        }
        return ;
    }
}