BFS (breadth first search) Input: root = [3,9,20,null,null,15,7] Output: [[3],[20,9],[15,7]] /** * 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 = f..
