07-Binary-Tree-Level-Order-Traversal-LC-102.js

/*
102. Binary Tree Level Order Traversal
Medium

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree [3,9,20,null,null,15,7],
    3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:
[
  [3],
  [9,20],
  [15,7]
]
*/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrder = function (root) {
    var result = [];

    if (root === null) {
        return result;
    }

    var queue = [];
    var temp = [];
    var curLvlCnt = 1;
    var nextLvlCnt = 0;

    queue.push(root);

    while (queue.length !== 0) {
        var p = queue.shift();
        temp.push(p.val);
        curLvlCnt--;

        if (p.left) {
            queue.push(p.left);
            nextLvlCnt++;
        }
        if (p.right) {
            queue.push(p.right);
            nextLvlCnt++;
        }

        if (curLvlCnt === 0) {
            result.push(temp);
            curLvlCnt = nextLvlCnt;
            nextLvlCnt = 0;
            temp = [];
        }
    }

    return result;
};