Leetcode - Binary Tree Level Order Traversal

Problem

Binary Tree Level Order Traversal

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).

이진트리 root가 주어 졌을 때, 계층의 순서대로 순회하는 값을 구하시오.
(좌측부터 우측으로, 계층별로)

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

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) {
    const result = []
    if(root === null) return result
    const queue = []
    queue.push(root)
    while(queue.length > 0) {
        let levelSize = queue.length
        const currentLevel = []
        for(let i = 0; i < levelSize; i++) {
           let currentNode = queue.shift()
           currentLevel.push(currentNode.val)
            if(currentNode.left !== null) queue.push(currentNode.left)
            if(currentNode.right !== null) queue.push(currentNode.right)
        }
        result.push(currentLevel)
    }
    return result

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