tree-level-order.js

var Tree = function() {
    this.root = null;
}

Tree.prototype.insert = function(node, data) {
    if (node == null){
    	node = new Node(data);
    }
 	else if (data < node.data){
        node.left  = this.insert(node.left, data);
    }
    else{
        node.right = this.insert(node.right, data);   
    }

    return node;
}

var Node = function(data) {
    this.data = data;
    this.left = null;
    this.right = null;
}

/* head ends */

process.stdin.resume();
process.stdin.setEncoding("ascii");
var input = "";
process.stdin.on("data", function (chunk) {
    input += chunk;
});
process.stdin.on("end", function () {
    // now we can read/parse input
});

function levelOrder(root) {
    
    const queue = [root];
    while(queue.length > 0) {
        
        const node = queue.shift();
        
        process.stdout.write(`${node.data} `);
        
        if (!!node.left) queue.push(node.left);
        
        if (!!node.right) queue.push(node.right);        
    }
}

/* tail begins */

process.stdin.resume();
process.stdin.setEncoding('ascii');

var _stdin = "";
var _stdin_array = "";
var _currentline = 0;

process.stdin.on('data', function(data) {
    _stdin += data;
});

process.stdin.on('end', function() {
    _stdin_array = _stdin.split("\n");
    solution();
});

function readLine() {
    return _stdin_array[_currentline++];
}

function solution() {

    var tree = new Tree();
    var n = parseInt(readLine());
    var m = readLine().split(" ").map(Number);
    for (var i=0; i<n; i++) {
        tree.root = tree.insert(tree.root, m[i]);
    }

    levelOrder(tree.root);
}