# Double-ended queue and Binary Tree implementations in Go

I’ve been checking out some old code of mine, which I’ve written years ago. Some of it dates back almost 20 years ago, and contains my first ever programming projects, which consist of some games written in C using the Allegro library, a program for locking binaries by doing a simple xor, and some implementations of various algorithms I’ve read about back then.

This old code has been recovered from some really old CD-ROM drives, and was quite interesting for me to go back in time and look at some of my first code. In a future post I’ll probably share more about my early programming projects, which I managed to recover from these CD-ROM drives.

At some point I thought about brushing up my algorithms and decided to implement some of them from scratch. It was a fun weekend exercise for me to go back to the basics and do a bit of linked lists, binary trees, queues, stacks, graphs, searching algorithms, sorting, etc. All in all, a pretty refreshing experience I would say.

Some of the code I managed to clean up and document, so I thought about publishing it as well on Github, in case this turns out useful to anyone else eventually.

The first library I’ve published is an implementation of double-ended queues in Go. Pretty simple and straightforward. Here’s how to install it.

``````go get -v gopkg.in/dnaeon/go-deque.v1
``````

You can find the code of the deque implementation in the dnaeon/go-deque repo.

The library supports generics, so you can use it with any type. Here’s an example of a deque, which stores integers.

``````package main

import (
"fmt"
"os"

deque "gopkg.in/dnaeon/go-deque.v1"
)

func main() {
d := deque.New[int]()

// Insert a few items to work with
// The deque looks like this: 5 4 1 2 3
d.PushBack(1)
d.PushBack(2)
d.PushBack(3)
d.PushFront(4)
d.PushFront(5)

fmt.Printf("deque len: %d\n", d.Length())

// Consume all items - front to back
for !d.IsEmpty() {
item, err := d.PopFront()
if err != nil {
fmt.Println(err)
os.Exit(1)
}
fmt.Printf("got item: %d\n", item)
}

fmt.Printf("deque len: %d\n", d.Length())
}
``````

Running above code produces the following output.

``````deque len: 5
got item: 5
got item: 4
got item: 1
got item: 2
got item: 3
deque len: 0
``````

The other library I’ve published is a simple, and generic implementation of binary trees in Go.

It implements various algorithms for binary trees, such as calculating height and size of the tree, walking the tree in in-, pre-, post- and level-order, and comes with a number of test predicates to check whether a tree is Perfect, Complete, Binary Search Tree, etc.

You can also generate a Dot representation of your tree and render it using graphviz.

You can find the full code in the dnaeon/go-binarytree repo. Here’s an example usage of the library.

``````package main

import (
"fmt"

binarytree "gopkg.in/dnaeon/go-binarytree.v1"
)

func main() {
root := binarytree.NewNode(10)
five := root.InsertLeft(5)
twenty := root.InsertRight(20)
five.InsertLeft(9)
five.InsertRight(18)
twenty.InsertLeft(3)
twenty.InsertRight(7)

fmt.Printf("height of tree: %d\n", root.Height())
fmt.Printf("size of the tree: %d\n", root.Size())
fmt.Printf("tree is balanced: %t\n", root.IsBalancedTree())
fmt.Printf("tree is complete: %t\n", root.IsCompleteTree())
fmt.Printf("tree is perfect: %t\n", root.IsPerfectTree())

// Function to be called while walking the tree, which simply
// prints the values of each visited node
walkFunc := func(n *binarytree.Node[int]) error {
fmt.Printf("%d ", n.Value)
return nil
}

fmt.Printf("in-order values: ")
root.WalkInOrder(walkFunc)
fmt.Println()

fmt.Printf("pre-order values: ")
root.WalkPreOrder(walkFunc)
fmt.Println()

fmt.Printf("post-orer values: ")
root.WalkPostOrder(walkFunc)
fmt.Println()

fmt.Printf("level-order values: ")
root.WalkLevelOrder(walkFunc)
fmt.Println()
}
``````

Running above code produces the following output.

``````height of tree: 2
size of the tree: 7
tree is balanced: true
tree is complete: true
tree is perfect: true
in-order values: 9 5 18 10 3 20 7
pre-order values: 10 5 9 18 20 3 7
post-orer values: 9 18 5 3 7 20 10
level-order values: 10 5 20 9 18 3 7
``````

We can generate the Dot representation of a tree using this code.

``````package main

import (
"os"

"gopkg.in/dnaeon/go-binarytree.v1"
)

func main() {
root := binarytree.NewNode(10)
five := root.InsertLeft(5)
twenty := root.InsertRight(20)
five.InsertLeft(9)
five.InsertRight(18)
twenty.InsertLeft(3)
twenty.InsertRight(7)

root.WriteDot(os.Stdout)
}
``````

Running above example produces an output similar to this one.

``````digraph {
node [color=lightblue fillcolor=lightblue fontcolor=black shape=record style="filled, rounded"]
824634441792 [label="<l>|<v> 10|<r>" ]
824634441792:l -> 824634441856:v
824634441792:r -> 824634441920:v
824634441856 [label="<l>|<v> 5|<r>" ]
824634441856:l -> 824634441984:v
824634441856:r -> 824634442048:v
824634441984 [label="<l>|<v> 9|<r>" ]
824634442048 [label="<l>|<v> 18|<r>" ]
824634441920 [label="<l>|<v> 20|<r>" ]
824634441920:l -> 824634442112:v
824634441920:r -> 824634442176:v
824634442112 [label="<l>|<v> 3|<r>" ]
824634442176 [label="<l>|<v> 7|<r>" ]
}
``````

Finally, we can render the binarytree using graphviz:

``````dot -Tsvg /path/to/file.dot -o /tmp/to/file.svg
``````

And here’s how our tree looks like.

Written on October 4, 2022