coded + unit tested

Author: Ram swaroop

src/me/ramswaroop/arrays/sorting/PancakeSort.java

@@ -0,0 +1,80 @@
+package me.ramswaroop.arrays.sorting;
+
+import java.util.Arrays;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 10/26/15
+ * @time: 9:20 PM
+ */
+public class PancakeSort {
+
+    /**
+     * Sorts the array {@param a} in-place in O(n^2) time complexity.
+     * <p/>
+     * This can also be seen as: Sort the array {@param a} using a method
+     * {@code reverse(int[] a, int end)} which reverses array {@code int[] a}
+     * from {@code 0} index till {@code end} index (both inclusive).
+     *
+     * @param a
+     */
+    public static void sort(int[] a) {
+
+        int maxIndex; // max element's index
+        int unsortedIndex = a.length - 1; // index till which elements are unsorted 
+
+        while (unsortedIndex > 0) {
+            maxIndex = 0;
+            // find max element's index
+            for (int j = 1; j <= unsortedIndex; j++) {
+                if (a[j] > a[maxIndex]) {
+                    maxIndex = j;
+                }
+            }
+            reverse(a, maxIndex); // bring the max element to the front 
+            reverse(a, unsortedIndex); // move the max element to its appropriate index
+            unsortedIndex--;
+        }
+    }
+
+    /**
+     * Reverses array {@param a} from {@code 0} index
+     * till {@code end} index.
+     *
+     * @param a
+     * @param end
+     */
+    public static void reverse(int[] a, int end) {
+        int temp;
+        for (int i = 0; i <= end / 2; i++) {
+            temp = a[i];
+            a[i] = a[end - i];
+            a[end - i] = temp;
+        }
+    }
+
+    public static void main(String a[]) {
+        int[] ar = {1, 2, 3, 4, 5, 6};
+        System.out.println(Arrays.toString(ar));
+        sort(ar);
+        System.out.println(Arrays.toString(ar));
+        ar = new int[]{3, 4, 7, 1, 9, 0};
+        System.out.println(Arrays.toString(ar));
+        sort(ar);
+        System.out.println(Arrays.toString(ar));
+        ar = new int[]{6, 5, 4, 3, 2, 1};
+        System.out.println(Arrays.toString(ar));
+        sort(ar);
+        System.out.println(Arrays.toString(ar));
+        ar = new int[]{};
+        System.out.println(Arrays.toString(ar));
+        sort(ar);
+        System.out.println(Arrays.toString(ar));
+        ar = new int[]{1};
+        System.out.println(Arrays.toString(ar));
+        sort(ar);
+        System.out.println(Arrays.toString(ar));
+    }
+}