Implement LinkedList

.gitignore

@@ -0,0 +1,42 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store

.idea/.gitignore

@@ -0,0 +1,8 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/gradle.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleHome" value="" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>

.idea/kotlinc.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="KotlinJpsPluginSettings">
+    <option name="version" value="1.9.23" />
+  </component>
+</project>

.idea/misc.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="FrameworkDetectionExcludesConfiguration">
+    <file type="web" url="file://$PROJECT_DIR$" />
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_20" default="true" project-jdk-name="corretto-20" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

build.gradle.kts

@@ -0,0 +1,21 @@
+plugins {
+    kotlin("jvm") version "1.9.23"
+}
+
+group = "dev.nuculabs.dsa"
+version = "1.0-SNAPSHOT"
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation(kotlin("test"))
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
+kotlin {
+    jvmToolchain(20)
+}

gradle.properties

@@ -0,0 +1 @@
+kotlin.code.style=official

gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,6 @@
+#Sat Apr 13 21:39:15 EEST 2024
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.5-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

gradlew

@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

readme.md

@@ -0,0 +1,6 @@
+# Data Structures and Algorithms
+
+This repository is my self study guide for data structures and algorithms. I implement them from scratch in Kotlin
+and then write unit test for them.
+
+What better way to learn a language and new concepts exists other than practicing them. 

settings.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("org.gradle.toolchains.foojay-resolver-convention") version "0.5.0"
+}
+rootProject.name = "DSA"
+

src/main/kotlin/Main.kt

@@ -0,0 +1,5 @@
+package dev.nuculabs.dsa
+
+fun main() {
+    println("hello world! See my blog at: blog.nuculabs.dev")
+}

src/main/kotlin/data_structures/linked_list/LinkedList.kt

@@ -0,0 +1,136 @@
+package dev.nuculabs.dsa.data_structures.linked_list
+
+/**
+ * Represents a node in the linked list.
+ */
+class Node<T>(val value: T, var next: Node<T>? = null)
+
+/**
+ * Represents a generic linked list.
+ */
+class LinkedList<T> : Iterable<Node<T>> {
+
+    private var head: Node<T>? = null
+    private var tail: Node<T>? = null
+    private var size: Int = 0
+
+    /**
+     * Returns the first value from the list.
+     */
+    fun getFirst(): T? {
+        return head?.value
+    }
+
+    /**
+     * Returns the last value from the list.
+     */
+    fun getLast(): T? {
+        return tail?.value
+    }
+
+    /**
+     * Appends value at the end of the list.
+     */
+    fun append(value: T) {
+        val newNode = Node(value, null)
+        if (head == null) {
+            head = newNode
+            tail = newNode
+        } else {
+            tail!!.next = newNode
+            tail = newNode
+        }
+        size += 1
+    }
+
+    /**
+     * Returns from the list
+     */
+    fun get(position: Int): T? {
+        var currentPosition = 0
+        var currentNode = head
+        while (currentPosition <= position && currentNode != null) {
+            if (currentPosition == position) {
+                return currentNode.value
+            }
+            currentNode = currentNode.next
+            currentPosition += 1
+        }
+        return null
+    }
+
+    /**
+     * Deletes an element from the linked list at the given position.
+     */
+    fun delete(position: Int) {
+        if (size == 0 || position < 0 || position >= size) {
+            return
+        }
+        // delete head
+        if (position == 0) {
+            head = head?.next
+            // if the list size is 1 then we don't have elements anymore
+            if (size == 1) {
+                tail = null
+            }
+            size -= 1
+            return
+        }
+        // delete anything from tail
+        var currentNode = head
+        var previousNode: Node<T>?
+        var currentPosition = 0
+        while (true) {
+            previousNode = currentNode
+            currentNode = currentNode?.next
+            currentPosition += 1
+            if (currentPosition == position) {
+                previousNode!!.next = currentNode?.next
+                if (currentPosition == size - 1) {
+                    tail = previousNode
+                }
+                break
+            }
+        }
+        size -= 1
+    }
+
+    /**
+     * Coverts the Linked List to a Java List.
+     */
+    fun toJavaList(): List<T> {
+        return this.toList().map { it.value }
+    }
+
+    /**
+     * Returns the size of the Linked List.
+     */
+    fun size(): Int {
+        return size
+    }
+
+    /**
+     * NodeIterator that iterates over linked list nodes.
+     */
+    class NodeIterator<T>(linkedList: LinkedList<T>) : Iterator<Node<T>> {
+        private var currentNode: Node<T>? = linkedList.head
+
+        override fun hasNext(): Boolean {
+            return currentNode != null
+        }
+
+        override fun next(): Node<T> {
+            val node = currentNode!!
+            currentNode = currentNode?.next
+            return node
+        }
+
+    }
+
+    /**
+     * Returns a list iterator.
+     */
+    override fun iterator(): Iterator<Node<T>> {
+        return NodeIterator(this)
+    }
+}

src/test/kotlin/data_structures/linked_list/LinkedListTest.kt

@@ -0,0 +1,167 @@
+package data_structures.linked_list
+
+import dev.nuculabs.dsa.data_structures.linked_list.LinkedList
+import org.junit.jupiter.api.Test
+
+import org.junit.jupiter.api.Assertions.*
+import kotlin.test.assertContentEquals
+
+
+class LinkedListTest {
+
+    @Test
+    fun getFirst_EmptyList() {
+        // Setup
+        val linkedList = LinkedList<String>()
+
+        // Test
+        assertNull(linkedList.getFirst())
+    }
+
+    @Test
+    fun getFirst() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        assertEquals("First", linkedList.getFirst())
+    }
+
+    @Test
+    fun getLast_Empty() {
+        // Setup
+        val linkedList = LinkedList<String>()
+
+        // Test
+        assertNull(linkedList.getLast())
+    }
+
+    @Test
+    fun getLast() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        assertEquals("Third", linkedList.getLast())
+    }
+
+    @Test
+    fun get() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        assertEquals("First", linkedList.get(0))
+        assertEquals("Second", linkedList.get(1))
+        assertEquals("Third", linkedList.get(2))
+        assertEquals(null, linkedList.get(3))
+    }
+
+    @Test
+    operator fun iterator() {
+        // Setup
+        val iteratorOutput = arrayOfNulls<String>(3)
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        linkedList.forEachIndexed { index, it ->
+            iteratorOutput[index] = it.value
+        }
+
+        // Assert
+        assertContentEquals(arrayOf("First", "Second", "Third"), iteratorOutput)
+    }
+
+    @Test
+    fun size() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        assertEquals(3, linkedList.size())
+    }
+
+    @Test
+    fun deleteHead() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        linkedList.delete(0)
+
+        // Assert
+        assertEquals(listOf("Second", "Third"), linkedList.toJavaList())
+        assertEquals("Second", linkedList.getFirst())
+        assertEquals("Third", linkedList.getLast())
+
+    }
+
+    @Test
+    fun deleteMiddle() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        linkedList.delete(1)
+
+        // Assert
+        assertEquals(listOf("First", "Third"), linkedList.toJavaList())
+        assertEquals("First", linkedList.getFirst())
+        assertEquals("Third", linkedList.getLast())
+
+    }
+
+
+    @Test
+    fun deleteLast() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        linkedList.delete(2)
+
+        // Assert
+        assertEquals(listOf("First", "Second"), linkedList.toJavaList())
+        assertEquals("First", linkedList.getFirst())
+        assertEquals("Second", linkedList.getLast())
+    }
+
+    @Test
+    fun toJavaList() {
+        // Setup
+        val linkedList = LinkedList<String>()
+        linkedList.append("First")
+        linkedList.append("Second")
+        linkedList.append("Third")
+
+        // Test
+        val result = linkedList.toJavaList()
+
+        // Assert
+        assertContentEquals(listOf("First", "Second", "Third"), result)
+    }
+}