Bryan C Guner

Posted on

# Tree Data Structure π²π΄π³π

### The Tree data structure (In Javascript)

The #data-structures series is a collection of posts about reimplemented data structures in JavaScript.

## Definition

A Tree is a widely used data structure that simulates a hierarchical tree structure, with a root value and subtrees of children with a parent node. A tree data structure can be defined recursively as a collection of nodes (starting at a root node), where each node is a data structure consisting of a value, together with a list of references to nodes (the "children"), with the constraints that no reference is duplicated, and none points to the root node. From Wikipedia

## Complexity

Average
Access Search Insertion Deletion
O(n) O(n) O(n) O(n)

To get a full overview of the time and space complexity of the Tree data structure, have a look to this excellent Big O cheat sheet.

## The code

``````function Node(data) {
this.data = data;
this.children = [];
}

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

var node = new Node(data);
var parent = toNodeData ? this.findBFS(toNodeData) : null;
if(parent) {
parent.children.push(node);
} else {
if(!this.root) {
this.root = node;
} else {
return 'Root node is already assigned';
}
}
};
Tree.prototype.remove = function(data) {
if(this.root.data === data) {
this.root = null;
}

var queue = [this.root];
while(queue.length) {
var node = queue.shift();
for(var i = 0; i < node.children.length; i++) {
if(node.children[i].data === data) {
node.children.splice(i, 1);
} else {
queue.push(node.children[i]);
}
}
}
};
Tree.prototype.contains = function(data) {
return this.findBFS(data) ? true : false;
};
Tree.prototype.findBFS = function(data) {
var queue = [this.root];
while(queue.length) {
var node = queue.shift();
if(node.data === data) {
return node;
}
for(var i = 0; i < node.children.length; i++) {
queue.push(node.children[i]);
}
}
return null;
};
Tree.prototype._preOrder = function(node, fn) {
if(node) {
if(fn) {
fn(node);
}
for(var i = 0; i < node.children.length; i++) {
this._preOrder(node.children[i], fn);
}
}
};
Tree.prototype._postOrder = function(node, fn) {
if(node) {
for(var i = 0; i < node.children.length; i++) {
this._postOrder(node.children[i], fn);
}
if(fn) {
fn(node);
}
}
};
Tree.prototype.traverseDFS = function(fn, method) {
var current = this.root;
if(method) {
this['_' + method](current, fn);
} else {
this._preOrder(current, fn);
}
};
Tree.prototype.traverseBFS = function(fn) {
var queue = [this.root];
while(queue.length) {
var node = queue.shift();
if(fn) {
fn(node);
}
for(var i = 0; i < node.children.length; i++) {
queue.push(node.children[i]);
}
}
};
Tree.prototype.print = function() {
if(!this.root) {
return console.log('No root node found');
}
var newline = new Node('|');
var queue = [this.root, newline];
var string = '';
while(queue.length) {
var node = queue.shift();
string += node.data.toString() + ' ';
if(node === newline && queue.length) {
queue.push(newline);
}
for(var i = 0; i < node.children.length; i++) {
queue.push(node.children[i]);
}
}
console.log(string.slice(0, -2).trim());
};
Tree.prototype.printByLevel = function() {
if(!this.root) {
return console.log('No root node found');
}
var newline = new Node('\n');
var queue = [this.root, newline];
var string = '';
while(queue.length) {
var node = queue.shift();
string += node.data.toString() + (node.data !== '\n' ? ' ' : '');
if(node === newline && queue.length) {
queue.push(newline);
}
for(var i = 0; i < node.children.length; i++) {
queue.push(node.children[i]);
}
}
console.log(string.trim());
};

var tree = new Tree();
tree.print(); // => ceo | cto cfo cmo | dev1 dev2 dev3 accountant
tree.printByLevel();  // => ceo \n cto cfo cmo \n dev1 dev2 dev3 accountant
console.log('tree contains dev1 is true:', tree.contains('dev1')); // => true
console.log('tree contains dev4 is false:', tree.contains('dev4')); // => false
console.log('--- BFS');
tree.traverseBFS(function(node) { console.log(node.data); }); // => ceo cto cfo cmo dev1 dev2 dev3 accountant
console.log('--- DFS preOrder');
tree.traverseDFS(function(node) { console.log(node.data); }, 'preOrder'); // => ceo cto dev1 dev2 dev3 cfo accountant cmo
console.log('--- DFS postOrder');
tree.traverseDFS(function(node) { console.log(node.data); }, 'postOrder'); // => dev1 dev2 dev3 cto accountant cfo cmo ceo
tree.remove('cmo');
tree.print(); // => ceo | cto cfo | dev1 dev2 dev3 accountant
tree.remove('cfo');
tree.print(); // => ceo | cto | dev1 dev2 dev3
``````