Added LLD projects

rate-limiter/.idea/.gitignore

@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml

rate-limiter/.idea/compiler.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <annotationProcessing>
+      <profile name="Maven default annotation processors profile" enabled="true">
+        <sourceOutputDir name="target/generated-sources/annotations" />
+        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
+        <outputRelativeToContentRoot value="true" />
+        <module name="rate-limiter" />
+      </profile>
+    </annotationProcessing>
+    <bytecodeTargetLevel>
+      <module name="rate-limiter" target="10" />
+    </bytecodeTargetLevel>
+  </component>
+</project>

rate-limiter/.idea/jarRepositories.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RemoteRepositoriesConfiguration">
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Central Repository" />
+      <option name="url" value="https://repo.maven.apache.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Maven Central repository" />
+      <option name="url" value="https://repo1.maven.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="jboss.community" />
+      <option name="name" value="JBoss Community repository" />
+      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
+    </remote-repository>
+  </component>
+</project>

rate-limiter/.idea/libraries/Maven__junit_junit_4_13.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: junit:junit:4.13">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/junit/junit/4.13/junit-4.13.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/junit/junit/4.13/junit-4.13-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/junit/junit/4.13/junit-4.13-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

rate-limiter/.idea/libraries/Maven__org_hamcrest_hamcrest_core_1_3.xml

@@ -0,0 +1,13 @@
+<component name="libraryTable">
+  <library name="Maven: org.hamcrest:hamcrest-core:1.3">
+    <CLASSES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar!/" />
+    </CLASSES>
+    <JAVADOC>
+      <root url="jar://$MAVEN_REPOSITORY$/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3-javadoc.jar!/" />
+    </JAVADOC>
+    <SOURCES>
+      <root url="jar://$MAVEN_REPOSITORY$/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

rate-limiter/.idea/misc.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="11" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>

rate-limiter/.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/rate-limiter.iml" filepath="$PROJECT_DIR$/rate-limiter.iml" />
+    </modules>
+  </component>
+</project>

rate-limiter/.idea/uiDesigner.xml

@@ -0,0 +1,124 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Palette2">
+    <group name="Swing">
+      <item class="com.intellij.uiDesigner.HSpacer" tooltip-text="Horizontal Spacer" icon="/com/intellij/uiDesigner/icons/hspacer.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="1" hsize-policy="6" anchor="0" fill="1" />
+      </item>
+      <item class="com.intellij.uiDesigner.VSpacer" tooltip-text="Vertical Spacer" icon="/com/intellij/uiDesigner/icons/vspacer.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="1" anchor="0" fill="2" />
+      </item>
+      <item class="javax.swing.JPanel" icon="/com/intellij/uiDesigner/icons/panel.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JScrollPane" icon="/com/intellij/uiDesigner/icons/scrollPane.png" removable="false" auto-create-binding="false" can-attach-label="true">
+        <default-constraints vsize-policy="7" hsize-policy="7" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JButton" icon="/com/intellij/uiDesigner/icons/button.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="0" fill="1" />
+        <initial-values>
+          <property name="text" value="Button" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JRadioButton" icon="/com/intellij/uiDesigner/icons/radioButton.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="RadioButton" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JCheckBox" icon="/com/intellij/uiDesigner/icons/checkBox.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="3" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="CheckBox" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JLabel" icon="/com/intellij/uiDesigner/icons/label.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="0" anchor="8" fill="0" />
+        <initial-values>
+          <property name="text" value="Label" />
+        </initial-values>
+      </item>
+      <item class="javax.swing.JTextField" icon="/com/intellij/uiDesigner/icons/textField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JPasswordField" icon="/com/intellij/uiDesigner/icons/passwordField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JFormattedTextField" icon="/com/intellij/uiDesigner/icons/formattedTextField.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1">
+          <preferred-size width="150" height="-1" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTextArea" icon="/com/intellij/uiDesigner/icons/textArea.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTextPane" icon="/com/intellij/uiDesigner/icons/textPane.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JEditorPane" icon="/com/intellij/uiDesigner/icons/editorPane.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JComboBox" icon="/com/intellij/uiDesigner/icons/comboBox.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="2" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JTable" icon="/com/intellij/uiDesigner/icons/table.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JList" icon="/com/intellij/uiDesigner/icons/list.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="2" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTree" icon="/com/intellij/uiDesigner/icons/tree.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3">
+          <preferred-size width="150" height="50" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JTabbedPane" icon="/com/intellij/uiDesigner/icons/tabbedPane.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3">
+          <preferred-size width="200" height="200" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JSplitPane" icon="/com/intellij/uiDesigner/icons/splitPane.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="3" hsize-policy="3" anchor="0" fill="3">
+          <preferred-size width="200" height="200" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JSpinner" icon="/com/intellij/uiDesigner/icons/spinner.png" removable="false" auto-create-binding="true" can-attach-label="true">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JSlider" icon="/com/intellij/uiDesigner/icons/slider.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="8" fill="1" />
+      </item>
+      <item class="javax.swing.JSeparator" icon="/com/intellij/uiDesigner/icons/separator.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="6" anchor="0" fill="3" />
+      </item>
+      <item class="javax.swing.JProgressBar" icon="/com/intellij/uiDesigner/icons/progressbar.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="0" fill="1" />
+      </item>
+      <item class="javax.swing.JToolBar" icon="/com/intellij/uiDesigner/icons/toolbar.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="6" anchor="0" fill="1">
+          <preferred-size width="-1" height="20" />
+        </default-constraints>
+      </item>
+      <item class="javax.swing.JToolBar$Separator" icon="/com/intellij/uiDesigner/icons/toolbarSeparator.png" removable="false" auto-create-binding="false" can-attach-label="false">
+        <default-constraints vsize-policy="0" hsize-policy="0" anchor="0" fill="1" />
+      </item>
+      <item class="javax.swing.JScrollBar" icon="/com/intellij/uiDesigner/icons/scrollbar.png" removable="false" auto-create-binding="true" can-attach-label="false">
+        <default-constraints vsize-policy="6" hsize-policy="0" anchor="0" fill="2" />
+      </item>
+    </group>
+  </component>
+</project>

rate-limiter/.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>

rate-limiter/pom.xml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>interviewready.io</groupId>
+    <artifactId>rate-limiter</artifactId>
+    <version>1.0</version>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>10</source>
+                    <target>10</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.13</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>

rate-limiter/rate-limiter.iml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module org.jetbrains.idea.maven.project.MavenProjectsManager.isMavenModule="true" type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" LANGUAGE_LEVEL="JDK_10">
+    <output url="file://$MODULE_DIR$/target/classes" />
+    <output-test url="file://$MODULE_DIR$/target/test-classes" />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$/src/main/java" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/src/test/java" isTestSource="true" />
+      <sourceFolder url="file://$MODULE_DIR$/src/main/resources" type="java-resource" />
+      <excludeFolder url="file://$MODULE_DIR$/target" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" scope="TEST" name="Maven: junit:junit:4.13" level="project" />
+    <orderEntry type="library" scope="TEST" name="Maven: org.hamcrest:hamcrest-core:1.3" level="project" />
+  </component>
+</module>

rate-limiter/src/main/java/TimerWheel.java

@@ -0,0 +1,77 @@
+import exceptions.RateLimitExceededException;
+import models.Request;
+import utils.Timer;
+
+import java.util.Map;
+import java.util.concurrent.*;
+
+public class TimerWheel {
+    private final int timeOutPeriod;
+    private final int capacityPerSlot;
+    private final TimeUnit timeUnit;
+    private final ArrayBlockingQueue<Request>[] slots;
+    private final Map<String, Integer> reverseIndex;
+    private final Timer timer;
+    private final ExecutorService[] threads;
+
+    public TimerWheel(final TimeUnit timeUnit,
+                      final int timeOutPeriod,
+                      final int capacityPerSlot,
+                      final Timer timer) {
+        this.timeUnit = timeUnit;
+        this.timeOutPeriod = timeOutPeriod;
+        this.capacityPerSlot = capacityPerSlot;
+        if (this.timeOutPeriod > 1000) {
+            throw new IllegalArgumentException();
+        }
+        this.slots = new ArrayBlockingQueue[this.timeOutPeriod];
+        this.threads = new ExecutorService[this.timeOutPeriod];
+        this.reverseIndex = new ConcurrentHashMap<>();
+        for (int i = 0; i < slots.length; i++) {
+            slots[i] = new ArrayBlockingQueue<>(capacityPerSlot);
+            threads[i] = Executors.newSingleThreadExecutor();
+        }
+        this.timer = timer;
+        final long timePerSlot = TimeUnit.MILLISECONDS.convert(1, timeUnit);
+        Executors.newSingleThreadScheduledExecutor()
+                .scheduleAtFixedRate(this::flushRequests,
+                        timePerSlot - (this.timer.getCurrentTimeInMillis() % timePerSlot),
+                        timePerSlot, TimeUnit.MILLISECONDS);
+    }
+
+    public Future<?> flushRequests() {
+        final int currentSlot = getCurrentSlot();
+        return threads[currentSlot].submit(() -> {
+            for (final Request request : slots[currentSlot]) {
+                if (timer.getCurrentTime(timeUnit) - request.getStartTime() >= timeOutPeriod) {
+                    slots[currentSlot].remove(request);
+                    reverseIndex.remove(request.getRequestId());
+                }
+            }
+        });
+    }
+
+    public Future<?> addRequest(final Request request) {
+        final int currentSlot = getCurrentSlot();
+        return threads[currentSlot].submit(() -> {
+            if (slots[currentSlot].size() >= capacityPerSlot) {
+                throw new RateLimitExceededException();
+            }
+            slots[currentSlot].add(request);
+            reverseIndex.put(request.getRequestId(), currentSlot);
+        });
+    }
+
+    public Future<?> evict(final String requestId) {
+        final int currentSlot = reverseIndex.get(requestId);
+        return threads[currentSlot].submit(() -> {
+            slots[currentSlot].remove(new Request(requestId, 0));
+            reverseIndex.remove(requestId);
+        });
+    }
+
+    private int getCurrentSlot() {
+        return (int) timer.getCurrentTime(timeUnit) % slots.length;
+    }
+}
+

rate-limiter/src/main/java/exceptions/RateLimitExceededException.java

@@ -0,0 +1,7 @@
+package exceptions;
+
+public class RateLimitExceededException extends IllegalStateException {
+    public RateLimitExceededException() {
+        super("Rate limit exceeded");
+    }
+}

rate-limiter/src/main/java/models/Request.java

@@ -0,0 +1,33 @@
+package models;
+
+import java.util.Objects;
+
+public class Request {
+    private final String requestId;
+    private final long startTime;
+
+    public Request(String requestId, long startTime) {
+        this.requestId = requestId;
+        this.startTime = startTime;
+    }
+
+    public String getRequestId() {
+        return requestId;
+    }
+
+    public long getStartTime() {
+        return startTime;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        return requestId.equals(((Request) o).requestId);
+    }
+
+    @Override
+    public int hashCode() {
+        return requestId.hashCode();
+    }
+}

rate-limiter/src/main/java/utils/Timer.java

@@ -0,0 +1,13 @@
+package utils;
+
+import java.util.concurrent.TimeUnit;
+
+public class Timer {
+    public long getCurrentTime(final TimeUnit timeUnit) {
+        return timeUnit.convert(getCurrentTimeInMillis(), TimeUnit.MILLISECONDS);
+    }
+
+    public long getCurrentTimeInMillis() {
+        return System.currentTimeMillis();
+    }
+}

rate-limiter/src/test/java/RateLimitTest.java

@@ -0,0 +1,74 @@
+import models.Request;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.concurrent.TimeUnit;
+
+public class RateLimitTest {
+
+    @Test
+    public void testDefaultBehaviour() throws Exception {
+        final TimeUnit timeUnit = TimeUnit.SECONDS;
+        final TestTimer timer = new TestTimer();
+        final TimerWheel timerWheel = new TimerWheel(timeUnit, 6, 3, timer);
+        timerWheel.addRequest(new Request("1", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("2", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("3", timer.getCurrentTime(timeUnit))).get();
+        Throwable exception = null;
+        try {
+            timerWheel.addRequest(new Request("4", timer.getCurrentTime(timeUnit))).get();
+        } catch (Exception e) {
+            exception = e.getCause();
+        }
+        Assert.assertNotNull(exception);
+        Assert.assertEquals("Rate limit exceeded", exception.getMessage());
+        tick(timeUnit, timer, timerWheel);
+        timerWheel.addRequest(new Request("4", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("5", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.evict("1").get();
+        timerWheel.evict("4").get();
+        timerWheel.addRequest(new Request("6", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("7", timer.getCurrentTime(timeUnit))).get();
+    }
+
+    @Test
+    public void testClearing() throws Exception {
+        final TimeUnit timeUnit = TimeUnit.SECONDS;
+        final TestTimer timer = new TestTimer();
+        final int timeOutPeriod = 6;
+        final TimerWheel timerWheel = new TimerWheel(timeUnit, timeOutPeriod, 3, timer);
+        timerWheel.addRequest(new Request("0", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("1", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("2", timer.getCurrentTime(timeUnit))).get();
+
+        Throwable exception = null;
+        try {
+            timerWheel.addRequest(new Request("3", timer.getCurrentTime(timeUnit))).get();
+        } catch (Exception e) {
+            exception = e.getCause();
+        }
+        Assert.assertNotNull(exception);
+        Assert.assertEquals("Rate limit exceeded", exception.getMessage());
+
+        for (int i = 0; i < timeOutPeriod; i++) {
+            tick(timeUnit, timer, timerWheel);
+        }
+        timerWheel.addRequest(new Request("4", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("5", timer.getCurrentTime(timeUnit))).get();
+        timerWheel.addRequest(new Request("6", timer.getCurrentTime(timeUnit))).get();
+
+        exception = null;
+        try {
+            timerWheel.addRequest(new Request("7", timer.getCurrentTime(timeUnit))).get();
+        } catch (Exception e) {
+            exception = e.getCause();
+        }
+        Assert.assertNotNull(exception);
+        Assert.assertEquals("Rate limit exceeded", exception.getMessage());
+    }
+
+    private void tick(TimeUnit timeUnit, TestTimer timer, TimerWheel timerWheel) throws Exception {
+        timer.setTime(timer.getCurrentTimeInMillis() + TimeUnit.MILLISECONDS.convert(1, timeUnit));
+        timerWheel.flushRequests().get();
+    }
+}

rate-limiter/src/test/java/TestTimer.java

@@ -0,0 +1,14 @@
+import utils.Timer;
+
+public class TestTimer extends Timer {
+    private long currentTime = System.currentTimeMillis();
+
+    @Override
+    public long getCurrentTimeInMillis() {
+        return currentTime;
+    }
+
+    public void setTime(final long currentTime) {
+        this.currentTime = currentTime;
+    }
+}