103. Binary Tree Zigzag Level Order Traversal

1/**
2 * Definition for a binary tree node.
3 * class TreeNode {
4 *     val: number
5 *     left: TreeNode | null
6 *     right: TreeNode | null
7 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
8 *         this.val = (val===undefined ? 0 : val)
9 *         this.left = (left===undefined ? null : left)
10 *         this.right = (right===undefined ? null : right)
11 *     }
12 * }
13 */
14
15function zigzagLevelOrder(root: TreeNode | null): number[][] {
16    if(!root) return [];
17    const res: number[][] = [];
18    const queue: TreeNode[] = [];
19    let left_to_right = true;
20    while(queue.length) {
21	    const level_size = queue.length;
22	    const level: number[] =[];
23	    for(let i =0; i < level_size;i++) {
24		    const node = queue.shift()!;
25		    level.push(node.val);
26		    if(node.left) queue.push(node.left)
27		    if(node.right)queue.push(node.right);
28	    }
29	    if(!left_to_right) level.reverse();
30	    res.push(level)
31	    left_to_right = !left_to_right
32    }
33    return res
34};