.

Author: jpolitz

ArrayExamples.java

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+
+
+public class ArrayExamples {
+
+  // Changes the input array to be in reversed order
+  static void reverseInPlace(int[] arr) {
+    for(int i = 0; i < arr.length; i += 1) {
+      arr[i] = arr[arr.length - i - 1];
+    }
+  }
+
+  // Returns a *new* array with all the elements of the input array in reversed
+  // order
+  static int[] reversed(int[] arr) {
+    int[] newArray = new int[arr.length];
+    for(int i = 0; i < arr.length; i += 1) {
+      arr[i] = newArray[arr.length - i - 1];
+    }
+    return arr;
+  }
+
+  // Averages the numbers in the array (takes the mean), but leaves out the
+  // lowest number when calculating. Returns 0 if there are no elements or just
+  // 1 element in the array
+  static double averageWithoutLowest(double[] arr) {
+    if(arr.length < 2) { return 0.0; }
+    double lowest = arr[0];
+    for(double num: arr) {
+      if(num < lowest) { lowest = num; }
+    }
+    double sum = 0;
+    for(double num: arr) {
+      if(num != lowest) { sum += num; }
+    }
+    return sum / (arr.length - 1);
+  }
+
+
+}
+

ArrayTests.java

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+import static org.junit.Assert.*;
+import org.junit.*;
+
+public class ArrayTests {
+	@Test 
+	public void testReverseInPlace() {
+    int[] input1 = { 3 };
+    ArrayExamples.reverseInPlace(input1);
+    assertArrayEquals(new int[]{ 3 }, input1);
+	}
+
+
+  @Test
+  public void testReversed() {
+    int[] input1 = { };
+    assertArrayEquals(new int[]{ }, ArrayExamples.reversed(input1));
+  }
+}

FileExample.java

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+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+public class FileExample {
+
+  /*
+
+  Given a File (which can represent either a file or directory), return a list
+  of all the files in that directory and all its subdirectories.
+
+  If given the path of a file (rather than a directory), it returns a list with
+  just that element.
+  
+  For example, for the following structure:
+
+  some-files/
+  |-  a.txt
+  |-  more-files/
+      |-  b.txt
+      |-  c.java
+  |-  even-more-files/
+      |-  d.java
+      |-  a.txt
+
+  Given new File("some-files/") as a parameter, we'd expect [some-files/a.txt,
+  some-files/more-files/b.txt, some-files/more-files/c.java,
+  some-files/even-more-files/d.java, some-files/even-more-files/a.txt] as results
+
+  Given new File("some-files/more-files") as a parameter, we'd expect
+  [some-files/more-files/b.txt, some-files/more-files/c.java] as results
+
+  Given new File("some-files/a.txt") as a parameter, we'd expect
+  [some-files/a.txt] and a result
+
+  See the File documentation here: https://docs.oracle.com/javase/8/docs/api/java/io/File.html
+
+  */
+
+	static List<File> getFiles(File start) throws IOException {
+	  File f = start;
+	  List<File> result = new ArrayList<>();
+	  result.add(start);
+	  if(f.isDirectory()) {
+      File[] paths = f.listFiles();
+      for(File subFile: paths) {
+        result.add(subFile);
+      }
+	  }
+	  return result;
+	}
+}
+
+

LectureExamples.java

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+class MainExample1 {
+	public static void main(String[] args) {
+    int current = 0;
+    while(current < args.length) {
+      System.out.println(args[current]);
+    }
+  }
+}
+
+class MainExample2 {
+	public static void main(String[] args) {
+    int length = args.length;
+    for(int i = 0; i < length; length += 1) {
+      System.out.println(args[i]);
+    }
+  }
+}
+
+class EvensExample {
+  static int sumEvenIndices(int[] nums) {
+    int sum = 0;
+    for(int i = 0; i < nums.length; i += 2) {
+      sum += nums[i + 1];
+    }
+    return sum;
+  }
+}
+
+class NumsExample {
+  static double reciprocal(int n) {
+    return 1 / n;
+  }
+  static double ratio(int n, int d) {
+    return n / d;
+  }
+  static double formula(int a, int b, int c) {
+    return ratio(a, b) * reciprocal(c);
+  }
+}

LinkedListExample.java

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+
+import java.util.NoSuchElementException;
+
+class Node {
+    int value;
+    Node next;
+    public Node(int value, Node next) {
+        this.value = value;
+        this.next = next;
+    }
+}
+class LinkedList {
+    Node root;
+    public LinkedList() {
+        this.root = null;
+    }
+    /**
+     * Adds the value to the _beginning_ of the list
+     * @param value
+     */
+    public void prepend(int value) {
+        // Just add at the beginning
+        this.root = new Node(value, this.root);
+    }
+    /**
+     * Adds the value to the _end_ of the list
+     * @param value
+     */
+    public void append(int value) {
+        if(this.root == null) {
+            this.root = new Node(value, null);
+            return;
+        }
+        // If it's just one element, add if after that one
+        Node n = this.root;
+        if(n.next == null) {
+            n.next = new Node(value, null);
+            return;
+        }
+        // Otherwise, loop until the end and add at the end with a null
+        while(n.next != null) {
+            n = n.next;
+            n.next = new Node(value, null);
+        }
+    }
+    /**
+     * @return the value of the first element in the list
+     */
+    public int first() {
+        return this.root.value;
+    }
+    /**
+     * @return the value of the last element in the list
+     */
+    public int last() {
+        Node n = this.root;
+        // If no such element, throw an exception
+        if(n == null) { throw new NoSuchElementException(); }
+        // If it's just one element, return its value
+        if(n.next == null) { return n.value; }
+        // Otherwise, search for the end of the list and return the last value
+        while(n.next != null) {
+            n = n.next;
+        }
+        return n.value;
+    }
+    /**
+     * @return a string representation of the list
+     */
+    public String toString() {
+        Node n = this.root;
+        String s = "";
+        while(n != null) {
+            s += n.value + " ";
+            n = n.next;
+        }
+        return s;
+    }
+    /**
+     * @return the number of elements in the list
+     */
+    public int length() {
+        Node n = this.root;
+        int i = 0;
+        while(n != null) {
+            i += 1;
+            n = n.next;
+        }
+        return i;
+    }
+}

ListExamples.java

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+import java.util.ArrayList;
+import java.util.List;
+
+interface StringChecker { boolean checkString(String s); }
+
+class ListExamples {
+
+  // Returns a new list that has all the elements of the input list for which
+  // the StringChecker returns true, and not the elements that return false, in
+  // the same order they appeared in the input list;
+  static List<String> filter(List<String> list, StringChecker sc) {
+    List<String> result = new ArrayList<>();
+    for(String s: list) {
+      if(sc.checkString(s)) {
+        result.add(0, s);
+      }
+    }
+    return result;
+  }
+
+
+  // Takes two sorted list of strings (so "a" appears before "b" and so on),
+  // and return a new list that has all the strings in both list in sorted order.
+  static List<String> merge(List<String> list1, List<String> list2) {
+    List<String> result = new ArrayList<>();
+    int index1 = 0, index2 = 0;
+    while(index1 < list1.size() && index2 < list2.size()) {
+      if(list1.get(index1).compareTo(list2.get(index2)) < 0) {
+        result.add(list1.get(index1));
+        index1 += 1;
+      }
+      else {
+        result.add(list2.get(index2));
+        index2 += 1;
+      }
+    }
+    while(index1 < list1.size()) {
+      result.add(list1.get(index1));
+      index1 += 1;
+    }
+    while(index2 < list2.size()) {
+      result.add(list2.get(index2));
+      index1 += 1;
+    }
+    return result;
+  }
+
+
+}

MethodsTests.java

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+import static org.junit.Assert.*;
+import org.junit.*;
+
+public class MethodsTests {
+  @Test 
+  public void testSumEvensLength4() {
+    int[] input1 = { 12, 13, 7, 2};
+    assertEquals(EvensExample.sumEvenIndices(input1), 19);
+  }
+  @Test 
+  public void testSumEvenLength5() {
+    int[] input1 = { 12, 13, 7, 2, 33};
+    assertEquals(EvensExample.sumEvenIndices(input1), 52);
+  }
+  @Test
+  public void testSumEvenLength6() {
+    int[] input1 = { 12, 13, 7, 8, 5, 3};
+    assertEquals(EvensExample.sumEvenIndices(input1), 24);
+  }
+}