Binary Tree Level Order Traversal LeetCode

binaryTreeLevelOrderTraversal.js

/*
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:
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
*/

/**
 * 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) {
    if (!root) return [];
    const arr = [root], result = [];
    
    while (arr.length) {
        const size = arr.length, values = [];
        
        for (let i = 0; i < size; i++) {
            const node = arr.shift()
            values.push(node.val)
            if (node.left) arr.push(node.left) 
            if (node.right) arr.push(node.right) 
        }
        result.push(values)
    }
    
    return result
};

const root = [3,9,20,null,null,15,7];
console.log(levelOrder(root));