use JUnit5 Extensions to redirect System.in and System.out and run benchmarks

added apache-commons libs
applied new code formatting rules

.idea/.name

@@ -0,0 +1 @@
+buy-and-sell-n-times

.idea/misc.xml

@@ -4,5 +4,5 @@
   <component name="JavaScriptSettings">
     <option name="languageLevel" value="ES6" />
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="false" project-jdk-name="11" project-jdk-type="JavaSDK" />
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="11" project-jdk-type="JavaSDK" />
 </project>

.idea/vcs.xml

@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="GitSharedSettings">
+    <option name="FORCE_PUSH_PROHIBITED_PATTERNS">
+      <list />
+    </option>
+  </component>
   <component name="VcsDirectoryMappings">
     <mapping directory="" vcs="Git" />
   </component>

build.gradle

@@ -16,6 +16,9 @@ allprojects {
     }
     
     dependencies {
+        implementation 'org.apache.commons:commons-lang3:3.10'
+        implementation 'org.apache.commons:commons-collections4:4.4'
+        implementation 'org.apache.commons:commons-math3:3.6.1'
         testImplementation 'org.junit.jupiter:junit-jupiter-api:5.6.0'
         testImplementation 'org.junit.jupiter:junit-jupiter-params:5.6.0'
         testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.6.0'

src/main/java/Solution.java

@@ -1,20 +1,62 @@
 import java.util.*;
-import java.io.*;
-import java.math.*;
+import java.util.stream.IntStream;
 
-/**
- * Template code to help you parse the standard input 
- * according to the problem statement.
- **/
 class Solution {
     
-	public static void main( String[] args ) {
-		Scanner in = new Scanner( System.in );
-		// read values with in.next...() methods
+    public static void main( String[] args ) {
+        // read values with in.next...() methods
+        var scanner   = new Scanner( System.in );
+        var sellCount = scanner.nextInt();
+        var prices = scanner.tokens()
+                            .mapToInt( Integer::valueOf )
+                            .toArray();
         
-		// code your solution here
+        // Write result with System.out.println()
+        System.out.println( maxProfits( sellCount, prices ));
+    }
+    
+    // code your solution here
+    // 0 - 1 | ... | x-sellCount - x  -->  0 - x-1 | ... | x-1 - x
+    private static int maxProfits( int sellCount, int[] prices ) {
+        return IntStream.range( 0, sellCount )
+                        .parallel()
+                        .map( sale -> {
+                            // recursion end condition
+                            if ( sellCount == 1 ) {
+                                return maxProfit( prices );
+                            }
+                            else {
+                                return IntStream.range( 2, prices.length )
+                                                .parallel()
+                                                .map( index -> {
+                                                    var       firstRange = Arrays.copyOfRange( prices, 0, index );
+                                                    final int max1       = maxProfit( firstRange );
+                    
+                                                    var secondRange = Arrays.copyOfRange( prices, index - 1,
+                                                                                          prices.length
+                                                                                        );
+                                                    // reduce range sizes recursively
+                                                    final int max2 = maxProfits( sellCount - 1, secondRange );
+                    
+                                                    return max1 + max2;
+                                                })
+                                                .max().orElse( 0 );
+                            }
+                        })
+                        .max().orElse( 0 );
+    }
+    
+    private static int maxProfit( int[] prices ) {
+        return IntStream.range( 0, prices.length )
+                        .map( index -> {
+                            var range = Arrays.copyOfRange( prices, Math.min( index + 1, prices.length - 1 ),
+                                                            prices.length
+                                                          );
+                            int max = IntStream.of( range ).max().orElse( 0 );
+                            // difference between current price and future maximum
+                            return max - prices[index];
+                        })
+                        .max().orElse( 0 );
+    }
     
-		// Write result with System.out.println()
-		System.out.println( "value" );
-	}
 }

src/test/java/BenchmarkExtension.java

@@ -0,0 +1,51 @@
+import org.junit.jupiter.api.extension.AfterAllCallback;
+import org.junit.jupiter.api.extension.AfterTestExecutionCallback;
+import org.junit.jupiter.api.extension.BeforeAllCallback;
+import org.junit.jupiter.api.extension.BeforeTestExecutionCallback;
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
+
+import java.util.logging.Logger;
+
+import static java.lang.System.currentTimeMillis;
+
+/**
+ * Based on TimingExtension from JUnit 5 user guide, and BenchmarkExtension from Nicolai Parlog
+ * https://github.com/CodeFX-org/demo-junit-5/blob/master/src/main/java/org/codefx/demo/junit5/BenchmarkExtension.java
+ */
+public class BenchmarkExtension implements BeforeAllCallback, BeforeTestExecutionCallback, AfterTestExecutionCallback, AfterAllCallback {
+    
+    private static final Namespace NAMESPACE = Namespace.create( BenchmarkExtension.class );
+    private static final Logger LOGGER = Logger.getLogger( BenchmarkExtension.class.getName() );
+        
+    @Override
+    public void beforeAll( ExtensionContext context ) {
+        context.getStore( NAMESPACE ).put( context.getRequiredTestClass(), currentTimeMillis() );
+    }
+    
+    @Override
+    public void afterAll( ExtensionContext context ) {
+        long launchTime  = context.getStore( NAMESPACE ).get( context.getRequiredTestClass(), long.class );
+        long elapsedTime = currentTimeMillis() - launchTime;
+        report( "Test class", context, elapsedTime );
+    }
+    
+    @Override
+    public void beforeTestExecution( ExtensionContext context ) {
+        context.getStore( NAMESPACE ).put( context.getRequiredTestMethod(), currentTimeMillis() );
+    }
+    
+    @Override
+    public void afterTestExecution( ExtensionContext context ) {
+        long launchTime  = context.getStore( NAMESPACE ).get( context.getRequiredTestMethod(), long.class );
+        long elapsedTime = currentTimeMillis() - launchTime;
+        report( "Test", context, elapsedTime );
+    }
+    
+    private static void report( String unit, ExtensionContext context, long elapsedTime ) {
+        String message = String.format( "%s '%s' took %d ms.", unit, context.getDisplayName(), elapsedTime );
+        context.publishReportEntry( "Benchmark", message );
+        LOGGER.info( message );
+    }
+    
+}

src/test/java/SolutionTest.java

@@ -1,77 +1,23 @@
-import java.io.*;
-
-import org.junit.jupiter.api.AfterAll;
-import org.junit.jupiter.api.BeforeAll;
+import com.github.stefanbirkner.systemlambda.SystemLambda;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.jupiter.api.extension.ExtendWith;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.CsvFileSource;
 
-import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.junit.jupiter.api.Assertions.*;
 
+@ExtendWith( BenchmarkExtension.class )
 class SolutionTest {
     
-	static long totalDuration;
-	
-	@BeforeAll
-	static void beforeAll() {
-		totalDuration = 0;
-	}
-	
-	@AfterAll
-	static void afterAll() {
-		System.out.println( String.format( "All solutions took %01d.%03d secs",  totalDuration / 1000,  totalDuration % 1000 ));
-	}
-	
-	@ParameterizedTest
-	@CsvFileSource( resources = "testdata.csv", numLinesToSkip = 1 )
-	void main( final String sellCount, final String input, final String expected ) throws IOException {
-		// keep original streams
-		InputStream oldIn = System.in;
-		PrintStream oldOut = System.out;
-		PrintStream oldErr = System.err;
-		ByteArrayOutputStream bos =  new ByteArrayOutputStream();
-		
-		try {
-			redirectStreams(
-					new ByteArrayInputStream( (sellCount + " " + input).getBytes( UTF_8 )),
-					new PrintStream( bos, true, UTF_8 ),
-					new PrintStream( new ByteArrayOutputStream(), true, UTF_8 )
-			);
-			
-			// start time tracking
-			long start = System.currentTimeMillis();
-			
-			Solution.main( new String[0] );
-			
-			// stop time tracking
-			long duration = System.currentTimeMillis() - start;
-			totalDuration += duration;
-			
-			// restore streams
-			redirectStreams( oldIn, oldOut, oldErr );
-			
-			System.out.println( String.format( "Solution took %01d.%03d secs",  duration / 1000,  duration % 1000 ));
-			
-			try (BufferedReader chk = new BufferedReader( new InputStreamReader( new ByteArrayInputStream( bos.toByteArray() ), UTF_8 ))) {
-				String[] expectedLines = expected.split( "\\s*[|]\\s*" );
+    @ParameterizedTest
+    @CsvFileSource( resources = "testdata.csv" )
+    void main( final String sellCount, final String input, final String expected ) throws Exception {
+        String output = SystemLambda.tapSystemOutNormalized( () -> 
+            SystemLambda.withTextFromSystemIn( sellCount + " " + input )
+                        .execute( () -> Solution.main( new String[0] ))
+        );
         
-				int lineCount = 0;
-				String line;
-				for ( ; (line = chk.readLine()) != null; lineCount++ ) {
-					assertEquals( expectedLines[ lineCount ], line );
-				}
-				assertEquals( expectedLines.length, lineCount );
-			}
-		}
-		finally {
-			// restore streams
-			redirectStreams( oldIn, oldOut, oldErr );
-		}
-	}
+        assertEquals( expected, StringUtils.chomp( output.trim() ));
+    }
     
-	static void redirectStreams( final InputStream input, final PrintStream output, final PrintStream error ) {
-		System.setIn( input );
-		System.setOut( output );
-		System.setErr( error );
-	}
 }

src/test/java/com/github/stefanbirkner/systemlambda/Statement.java

@@ -0,0 +1,15 @@
+package com.github.stefanbirkner.systemlambda;
+
+/**
+ * Code that should be executed by on of the methods of {@link SystemLambda}.
+ * This code may throw an {@link Exception}. Therefore we cannot use
+ * {@link Runnable}.
+ */
+public interface Statement {
+    /**
+     * Execute the statement.
+     *
+     * @throws Exception the statement may throw an arbitrary exception.
+     */
+    void execute() throws Exception;
+}

src/test/resources/testdata.csv

@@ -1,4 +1,3 @@
-sellCount, prices, maxProfit
 2, 12 11 13 9 12 8 14 13 15, 10
 3, 12 11 13 9 12 8 14 13 15, 12
 2, 310 315 275 295 260 270 290 230 255 250, 55