637. Average of Levels in Binary Tree

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 averageOfLevels(root: TreeNode | null): number[] {
16    const res: number[] = [];
17    if(!root) return [];
18    const queue: TreeNode[] = [root];
19    while(queue.length) {
20	    const level_size = queue.length;
21	    let sum = 0;
22	    for(let i =0 ; i < level_size; i++) {
23		    const node = queue.shift()!;
24			   sum += node.val;
25			   if(node.left) queue.push(node.left);
26			   if(node.right) queue.push(node.right);
27	    }
28	    res.push(sum / level_size)
29    }
30    return res;
31};