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<title>Algorithms and Data Structures in Go - Part 1</title>
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<h1 style='display: inline'>Algorithms and Data Structures in Go - Part 1</h1><br />
<br />
<span class='quote'>Published at 2023-04-09T22:31:42+03:00</span><br />
<br />
<pre>
,_---~~~~~----._
_,,_,*^____ _____``*g*\"*,
/ __/ /' ^. / \ ^@q f
[ @f | @)) | | @)) l 0 _/
\`/ \~____ / __ \_____/ \
| _l__l_ I
} [______] I
] | | | |
] ~ ~ |
| |
| |
</pre>
<br />
<span>This is the first blog post about my Algorithms and Data Structures in Go series. I am not a Software Developer in my day job. In my current role, programming and scripting skills are desirable but not mandatory. I have been learning about Data Structures and Algorithms many years ago at University. I thought it would be fun to revisit/refresh my knowledge here and implement many of the algorithms in Go.</span><br />
<br />
<a class='textlink' href='./2023-04-09-algorithms-and-data-structures-in-golang-part-1.html'>2023-04-09 Algorithms and Data Structures in Go - Part 1 (You are currently reading this)</a><br />
<br />
<span>This post is about setting up some basic data structures and methods for this blog series. I promise, everything will be easy to follow in this post. It will become more interesting later in this series.</span><br />
<br />
<h2 style='display: inline'>Type constraints</h2><br />
<br />
<span>First, the package <span class='inlinecode'>ds</span> (data structures) defines the <span class='inlinecode'>types.go</span>. All examples will either operate on the <span class='inlinecode'>Integer</span> or <span class='inlinecode'>Number</span> type:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">package</font></b> ds
<b><font color="#0000FF">import</font></b> <font color="#990000">(</font>
<font color="#FF0000">"golang.org/x/exp/constraints"</font>
<font color="#990000">)</font>
<b><font color="#0000FF">type</font></b> Integer <b><font color="#0000FF">interface</font></b> <font color="#FF0000">{</font>
constraints<font color="#990000">.</font>Integer
<font color="#FF0000">}</font>
<b><font color="#0000FF">type</font></b> Number <b><font color="#0000FF">interface</font></b> <font color="#FF0000">{</font>
constraints<font color="#990000">.</font>Integer <font color="#990000">|</font> constraints<font color="#990000">.</font>Float
<font color="#FF0000">}</font>
</pre>
<br />
<h2 style='display: inline'>ArrayList</h2><br />
<br />
<span>Next comes the <span class='inlinecode'>arraylist.go</span>, which defines the underlying data structure all the algorithms of this series will use. <span class='inlinecode'>ArrayList</span> is just a type alias of a Go array (or slice) with custom methods on it:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">package</font></b> ds
<b><font color="#0000FF">import</font></b> <font color="#990000">(</font>
<font color="#FF0000">"fmt"</font>
<font color="#FF0000">"math/rand"</font>
<font color="#FF0000">"strings"</font>
<font color="#990000">)</font>
<b><font color="#0000FF">type</font></b> ArrayList<font color="#990000">[</font>V Number<font color="#990000">]</font> <font color="#990000">[]</font>V
<b><font color="#0000FF">func</font></b> NewArrayList<font color="#990000">[</font>V Number<font color="#990000">](</font>l int<font color="#990000">)</font> ArrayList<font color="#990000">[</font>V<font color="#990000">]</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">return</font></b> <b><font color="#000000">make</font></b><font color="#990000">(</font>ArrayList<font color="#990000">[</font>V<font color="#990000">],</font> l<font color="#990000">)</font>
<font color="#FF0000">}</font>
</pre>
<br />
<span>As you can see, the code uses Go generics, which I refactored recently. Besides the default constructor (which only returns an empty <span class='inlinecode'>ArrayList</span> with a given capacity), there are also a bunch of special constructors. <span class='inlinecode'>NewRandomArrayList</span> is returning an <span class='inlinecode'>ArrayList</span> with random numbers, <span class='inlinecode'>NewAscendingArrayList</span> and <span class='inlinecode'>NewDescendingArrayList</span> are returning <span class='inlinecode'>ArrayList</span>s in either ascending or descending order. They all will be used later on for testing and benchmarking the algorithms.</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">func</font></b> NewRandomArrayList<font color="#990000">[</font>V Number<font color="#990000">](</font>l<font color="#990000">,</font> max int<font color="#990000">)</font> ArrayList<font color="#990000">[</font>V<font color="#990000">]</font> <font color="#FF0000">{</font>
a <font color="#990000">:=</font> <b><font color="#000000">make</font></b><font color="#990000">(</font>ArrayList<font color="#990000">[</font>V<font color="#990000">],</font> l<font color="#990000">)</font>
<b><font color="#0000FF">for</font></b> i <font color="#990000">:=</font> <font color="#993399">0</font><font color="#990000">;</font> i <font color="#990000"><</font> l<font color="#990000">;</font> i<font color="#990000">++</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">if</font></b> max <font color="#990000">></font> <font color="#993399">0</font> <font color="#FF0000">{</font>
a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000">=</font> <b><font color="#000000">V</font></b><font color="#990000">(</font>rand<font color="#990000">.</font><b><font color="#000000">Intn</font></b><font color="#990000">(</font>max<font color="#990000">))</font>
<b><font color="#0000FF">continue</font></b>
<font color="#FF0000">}</font>
a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000">=</font> <b><font color="#000000">V</font></b><font color="#990000">(</font>rand<font color="#990000">.</font><b><font color="#000000">Int</font></b><font color="#990000">())</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> a
<font color="#FF0000">}</font>
<b><font color="#0000FF">func</font></b> NewAscendingArrayList<font color="#990000">[</font>V Number<font color="#990000">](</font>l int<font color="#990000">)</font> ArrayList<font color="#990000">[</font>V<font color="#990000">]</font> <font color="#FF0000">{</font>
a <font color="#990000">:=</font> <b><font color="#000000">make</font></b><font color="#990000">(</font>ArrayList<font color="#990000">[</font>V<font color="#990000">],</font> l<font color="#990000">)</font>
<b><font color="#0000FF">for</font></b> i <font color="#990000">:=</font> <font color="#993399">0</font><font color="#990000">;</font> i <font color="#990000"><</font> l<font color="#990000">;</font> i<font color="#990000">++</font> <font color="#FF0000">{</font>
a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000">=</font> <b><font color="#000000">V</font></b><font color="#990000">(</font>i<font color="#990000">)</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> a
<font color="#FF0000">}</font>
<b><font color="#0000FF">func</font></b> NewDescendingArrayList<font color="#990000">[</font>V Number<font color="#990000">](</font>l int<font color="#990000">)</font> ArrayList<font color="#990000">[</font>V<font color="#990000">]</font> <font color="#FF0000">{</font>
a <font color="#990000">:=</font> <b><font color="#000000">make</font></b><font color="#990000">(</font>ArrayList<font color="#990000">[</font>V<font color="#990000">],</font> l<font color="#990000">)</font>
j <font color="#990000">:=</font> l <font color="#990000">-</font> <font color="#993399">1</font>
<b><font color="#0000FF">for</font></b> i <font color="#990000">:=</font> <font color="#993399">0</font><font color="#990000">;</font> i <font color="#990000"><</font> l<font color="#990000">;</font> i<font color="#990000">++</font> <font color="#FF0000">{</font>
a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000">=</font> <b><font color="#000000">V</font></b><font color="#990000">(</font>j<font color="#990000">)</font>
j<font color="#990000">--</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> a
<font color="#FF0000">}</font>
</pre>
<br />
<h2 style='display: inline'>Helper methods</h2><br />
<br />
<span>The <span class='inlinecode'>FirstN</span> method only returns the first N elements of the <span class='inlinecode'>ArrayList</span>. This is useful for printing out only parts of the data structure:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">func</font></b> <font color="#990000">(</font>a ArrayList<font color="#990000">[</font>V<font color="#990000">])</font> <b><font color="#000000">FirstN</font></b><font color="#990000">(</font>n int<font color="#990000">)</font> <font color="#009900">string</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">var</font></b> sb strings<font color="#990000">.</font>Builder
j <font color="#990000">:=</font> n
l <font color="#990000">:=</font> <b><font color="#000000">len</font></b><font color="#990000">(</font>a<font color="#990000">)</font>
<b><font color="#0000FF">if</font></b> j <font color="#990000">></font> l <font color="#FF0000">{</font>
j <font color="#990000">=</font> l
<font color="#FF0000">}</font>
<b><font color="#0000FF">for</font></b> i <font color="#990000">:=</font> <font color="#993399">0</font><font color="#990000">;</font> i <font color="#990000"><</font> j<font color="#990000">;</font> i<font color="#990000">++</font> <font color="#FF0000">{</font>
fmt<font color="#990000">.</font><b><font color="#000000">Fprintf</font></b><font color="#990000">(&</font>sb<font color="#990000">,</font> <font color="#FF0000">"%v "</font><font color="#990000">,</font> a<font color="#990000">[</font>i<font color="#990000">])</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">if</font></b> j <font color="#990000"><</font> l <font color="#FF0000">{</font>
fmt<font color="#990000">.</font><b><font color="#000000">Fprintf</font></b><font color="#990000">(&</font>sb<font color="#990000">,</font> <font color="#FF0000">"... "</font><font color="#990000">)</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> sb<font color="#990000">.</font><b><font color="#000000">String</font></b><font color="#990000">()</font>
<font color="#FF0000">}</font>
</pre>
<br />
<span>The <span class='inlinecode'>Sorted</span> method checks whether the <span class='inlinecode'>ArrayList</span> is sorted. This will be used by the unit tests later on:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">func</font></b> <font color="#990000">(</font>a ArrayList<font color="#990000">[</font>V<font color="#990000">])</font> <b><font color="#000000">Sorted</font></b><font color="#990000">()</font> <font color="#009900">bool</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">for</font></b> i <font color="#990000">:=</font> <b><font color="#000000">len</font></b><font color="#990000">(</font>a<font color="#990000">)</font> <font color="#990000">-</font> <font color="#993399">1</font><font color="#990000">;</font> i <font color="#990000">></font> <font color="#993399">0</font><font color="#990000">;</font> i<font color="#990000">--</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">if</font></b> a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000"><</font> a<font color="#990000">[</font>i<font color="#990000">-</font><font color="#993399">1</font><font color="#990000">]</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">return</font></b> false
<font color="#FF0000">}</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> true
<font color="#FF0000">}</font>
</pre>
<br />
<span>And the last utility method used is <span class='inlinecode'>Swap</span>, which allows swapping the values of two indices in the <span class='inlinecode'>ArrayList</span>:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">func</font></b> <font color="#990000">(</font>a ArrayList<font color="#990000">[</font>V<font color="#990000">])</font> <b><font color="#000000">Swap</font></b><font color="#990000">(</font>i<font color="#990000">,</font> j int<font color="#990000">)</font> <font color="#FF0000">{</font>
aux <font color="#990000">:=</font> a<font color="#990000">[</font>i<font color="#990000">]</font>
a<font color="#990000">[</font>i<font color="#990000">]</font> <font color="#990000">=</font> a<font color="#990000">[</font>j<font color="#990000">]</font>
a<font color="#990000">[</font>j<font color="#990000">]</font> <font color="#990000">=</font> aux
<font color="#FF0000">}</font>
</pre>
<br />
<h2 style='display: inline'>Sleep sort</h2><br />
<br />
<span>Let's implement our first algorithm, sleep sort. Sleep sort is a non-traditional and unconventional sorting algorithm based on the idea of waiting a certain amount of time corresponding to the value of each element in the input <span class='inlinecode'>ArrayList</span>. It's more of a fun, creative concept rather than an efficient or practical sorting technique. This is not a sorting algorithm you would use in any production code. As you can imagine, it is quite an inefficient sorting algorithm (it's only listed here as a warm-up exercise). This sorting method may also return false results depending on how the Goroutines are scheduled by the Go runtime. </span><br />
<br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">package</font></b> sort
<b><font color="#0000FF">import</font></b> <font color="#990000">(</font>
<font color="#FF0000">"codeberg.org/snonux/algorithms/ds"</font>
<font color="#FF0000">"sync"</font>
<font color="#FF0000">"time"</font>
<font color="#990000">)</font>
<b><font color="#0000FF">func</font></b> Sleep<font color="#990000">[</font>V ds<font color="#990000">.</font>Integer<font color="#990000">](</font>a ds<font color="#990000">.</font>ArrayList<font color="#990000">[</font>V<font color="#990000">])</font> ds<font color="#990000">.</font>ArrayList<font color="#990000">[</font>V<font color="#990000">]</font> <font color="#FF0000">{</font>
sorted <font color="#990000">:=</font> ds<font color="#990000">.</font>NewArrayList<font color="#990000">[</font>V<font color="#990000">](</font><b><font color="#000000">len</font></b><font color="#990000">(</font>a<font color="#990000">))</font>
numCh <font color="#990000">:=</font> <b><font color="#000000">make</font></b><font color="#990000">(</font><b><font color="#0000FF">chan</font></b> V<font color="#990000">)</font>
<b><font color="#0000FF">var</font></b> wg sync<font color="#990000">.</font>WaitGroup
wg<font color="#990000">.</font><b><font color="#000000">Add</font></b><font color="#990000">(</font><b><font color="#000000">len</font></b><font color="#990000">(</font>a<font color="#990000">))</font>
<b><font color="#0000FF">go</font></b> <b><font color="#0000FF">func</font></b><font color="#990000">()</font> <font color="#FF0000">{</font>
wg<font color="#990000">.</font><b><font color="#000000">Wait</font></b><font color="#990000">()</font>
<b><font color="#000000">close</font></b><font color="#990000">(</font>numCh<font color="#990000">)</font>
<font color="#FF0000">}</font><font color="#990000">()</font>
<b><font color="#0000FF">for</font></b> _<font color="#990000">,</font> num <font color="#990000">:=</font> <b><font color="#0000FF">range</font></b> a <font color="#FF0000">{</font>
<b><font color="#0000FF">go</font></b> <b><font color="#0000FF">func</font></b><font color="#990000">(</font>num V<font color="#990000">)</font> <font color="#FF0000">{</font>
<b><font color="#0000FF">defer</font></b> wg<font color="#990000">.</font><b><font color="#000000">Done</font></b><font color="#990000">()</font>
time<font color="#990000">.</font><b><font color="#000000">Sleep</font></b><font color="#990000">(</font>time<font color="#990000">.</font><b><font color="#000000">Duration</font></b><font color="#990000">(</font>num<font color="#990000">)</font> <font color="#990000">*</font> time<font color="#990000">.</font>Second<font color="#990000">)</font>
numCh <font color="#990000"><-</font> num
<font color="#FF0000">}</font><font color="#990000">(</font>num<font color="#990000">)</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">for</font></b> num <font color="#990000">:=</font> <b><font color="#0000FF">range</font></b> numCh <font color="#FF0000">{</font>
sorted <font color="#990000">=</font> <b><font color="#000000">append</font></b><font color="#990000">(</font>sorted<font color="#990000">,</font> num<font color="#990000">)</font>
<font color="#FF0000">}</font>
<b><font color="#0000FF">return</font></b> sorted
<font color="#FF0000">}</font>
</pre>
<br />
<span>This Go code implements the sleep sort algorithm using generics and goroutines. The main function <span class='inlinecode'>Sleep[V ds.Integer](a ds.ArrayList[V]) ds.ArrayList[V]</span> takes a generic <span class='inlinecode'>ArrayList</span> as input and returns a sorted <span class='inlinecode'>ArrayList</span>. The code creates a separate goroutine for each element in the input array, sleeps for a duration proportional to the element's value, and then sends the element to a channel. Another goroutine waits for all the sleeping goroutines to finish and then closes the channel. The sorted result <span class='inlinecode'>ArrayList</span> is constructed by appending the elements received from the channel in the order they arrive. The <span class='inlinecode'>sync.WaitGroup</span> is used to synchronize goroutines and ensure that all of them have completed before closing the channel.</span><br />
<br />
<h3 style='display: inline'>Testing</h3><br />
<br />
<span>For testing, we only allow values up to 10, as otherwise, it would take too long to finish:</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre><b><font color="#0000FF">package</font></b> sort
<b><font color="#0000FF">import</font></b> <font color="#990000">(</font>
<font color="#FF0000">"fmt"</font>
<font color="#FF0000">"testing"</font>
<font color="#FF0000">"codeberg.org/snonux/algorithms/ds"</font>
<font color="#990000">)</font>
<b><font color="#0000FF">func</font></b> <b><font color="#000000">TestSleepSort</font></b><font color="#990000">(</font>t <font color="#990000">*</font>testing<font color="#990000">.</font>T<font color="#990000">)</font> <font color="#FF0000">{</font>
a <font color="#990000">:=</font> ds<font color="#990000">.</font>NewRandomArrayList<font color="#990000">[</font>int<font color="#990000">](</font><font color="#993399">10</font><font color="#990000">,</font> <font color="#993399">10</font><font color="#990000">)</font>
a <font color="#990000">=</font> <b><font color="#000000">Sleep</font></b><font color="#990000">(</font>a<font color="#990000">)</font>
<b><font color="#0000FF">if</font></b> <font color="#990000">!</font>a<font color="#990000">.</font><b><font color="#000000">Sorted</font></b><font color="#990000">()</font> <font color="#FF0000">{</font>
t<font color="#990000">.</font><b><font color="#000000">Errorf</font></b><font color="#990000">(</font><font color="#FF0000">"Array not sorted: %v"</font><font color="#990000">,</font> a<font color="#990000">)</font>
<font color="#FF0000">}</font>
<font color="#FF0000">}</font>
</pre>
<br />
<span>As you can see, it takes <span class='inlinecode'>9s</span> here for the algorithm to finish (which is the highest value in the <span class='inlinecode'>ArrayList</span>):</span><br />
<br />
<!-- Generator: GNU source-highlight 3.1.9
by Lorenzo Bettini
http://www.lorenzobettini.it
http://www.gnu.org/software/src-highlite -->
<pre>❯ go <b><font color="#0000FF">test</font></b> <font color="#990000">.</font>/sort -v -run SleepSort
<font color="#990000">===</font> RUN TestSleepSort
--- PASS<font color="#990000">:</font> TestSleepSort <font color="#990000">(</font><font color="#993399">9</font><font color="#990000">.</font>00s<font color="#990000">)</font>
PASS
ok codeberg<font color="#990000">.</font>org/snonux/algorithms/sort <font color="#993399">9</font><font color="#990000">.</font>002s
</pre>
<br />
<span>I won't write any benchmark for sleep sort; that will be done for the algorithms to come in this series :-).</span><br />
<br />
<span>E-Mail your comments to <span class='inlinecode'>paul@nospam.buetow.org</span> :-)</span><br />
<br />
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