Binary Tree Level Order Traversal
Description
Given the root
of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).
Example 1:
![](https://assets.leetcode.com/uploads/2021/02/19/tree1.jpg)
Input: root = [3,9,20,null,null,15,7] Output: [[3],[9,20],[15,7]]
Example 2:
Input: root = [1] Output: [[1]]
Example 3:
Input: root = [] Output: []
Constraints:
- The number of nodes in the tree is in the range
[0, 2000]
. -1000 <= Node.val <= 1000
Solution(javascript)
/**
* 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 levelOrder = function(root) {
let result = [];
let queue = [root];
while (queue[0]) {
let queueLength = queue.length
let level = [];
for (let i = 0; i < queueLength; i++) {
let current = queue.shift();
level.push(current.val);
if (current.left ) queue.push(current.left);
if (current.right) queue.push(current.right);
}
result.push(level);
}
return result;
};