/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var zigzagLevelOrder = function(root) {
    if (!root) return [];
    let q = [];
    let result = [];
    
    q.push(root);
    let level = 0;
    
    while (q.length !== 0) {
        let nodesInLevel = q.length;
        let order = [];
        for (let i = 0; i < nodesInLevel; i++) {
            let curNode = q.shift();
            if (curNode.left) q.push(curNode.left);
            if (curNode.right) q.push(curNode.right);
            order.push(curNode.val);
            
        }
        level % 2 === 0 ? result.push(order):
            result.push(order.reverse())
        level++;
    }
    
    return result;
};