Add Ex 23.03

Author: Harry Dulaney

ch_23/Exercise23_03.java

@@ -0,0 +1,124 @@
+package ch_23;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+/**
+ * 23.3 (Generic quick sort) Write the following two generic methods using quick sort.
+ * The first method sorts the elements using the Comparable interface and the
+ * second uses the Comparator interface.
+ * public static <E extends Comparable<E>>
+ * void quickSort(E[] list)
+ * public static <E> void quickSort(E[] list,
+ * Comparator<? super E> comparator)
+ */
+public class Exercise23_03 {
+
+    public static void main(String[] args) {
+        Integer[] arr = new Integer[]{23, 25, 7, 14, 85, 65};
+        quickSort(arr);
+        System.out.println(Arrays.toString(arr));
+
+        Integer[] arr2 = new Integer[]{3, 2, 7, 4, 8, 6, 1, 7};
+        quickSort(arr2, Integer::compareTo);
+        System.out.println(Arrays.toString(arr2));
+
+    }
+
+    // Using Comparable
+    public static <E extends Comparable<E>> void quickSort(E[] list) {
+        quickSort(list, 0, list.length - 1);
+    }
+
+    public static <E extends Comparable<E>> void quickSort(E[] list, int first, int last) {
+        if (last > first) {
+            int pivotIndex = partition(list, first, last);
+            quickSort(list, first, pivotIndex - 1);
+            quickSort(list, pivotIndex + 1, last);
+        }
+    }
+
+    public static <E extends Comparable<E>> int partition(E[] list, int first, int last) {
+        E pivot = list[first]; // Choose the first element as the pivot
+        int low = first + 1; // Index for forward search
+        int high = last; // Index for backward search
+
+        while (high > low) {
+            // Search forward from left
+            while (low <= high && list[low].compareTo(pivot) <= 0) low++;
+
+            // Search backward from right
+            while (low <= high && list[high].compareTo(pivot) > 0) high--;
+
+            // Swap two elements in the list
+            if (high > low) {
+                E temp = list[high];
+                list[high] = list[low];
+                list[low] = temp;
+            }
+        }
+
+        while (high > first && list[high].compareTo(pivot) >= 0)
+            high--;
+
+        // Swap pivot with list[high]
+        if (pivot.compareTo(list[high]) > 0) {
+            list[first] = list[high];
+            list[high] = pivot;
+            return high;
+        } else {
+            return first;
+        }
+    }
+
+    // Using Comparator
+    public static <E> void quickSort(E[] list,
+                                     Comparator<? super E> comparator) {
+        quickSort(list, 0, list.length - 1, comparator);
+
+
+    }
+
+    // Using Comparator
+    public static <E> void quickSort(E[] list, int first, int last,
+                                     Comparator<? super E> comparator) {
+        if (last > first) {
+            int pivotIndex;
+            // find pivot index
+            E pivot = list[first]; // Choose the first element as the pivot
+            int low = first + 1; // Index for forward search
+            int high = last; // Index for backward search
+
+            while (high > low) {
+                // Search forward from left
+                while (low <= high && comparator.compare(list[low], pivot) <= 0) low++;
+
+                // Search backward from right
+                while (low <= high && comparator.compare(list[high], pivot) > 0) high--;
+
+                // Swap two elements in the list
+                if (high > low) {
+                    E temp = list[high];
+                    list[high] = list[low];
+                    list[low] = temp;
+                }
+            }
+
+            while (high > first && comparator.compare(list[high], pivot) >= 0)
+                high--;
+
+            // Swap pivot with list[high]
+            if (comparator.compare(pivot, list[high]) > 0) {
+                list[first] = list[high];
+                list[high] = pivot;
+                pivotIndex = high;
+            } else {
+                pivotIndex = first;
+            }
+
+            quickSort(list, first, pivotIndex - 1, comparator);
+            quickSort(list, pivotIndex + 1, last, comparator);
+        }
+    }
+
+}