Code improvements

module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedQueue.java

@@ -25,11 +25,12 @@ public class LinkedQueue<E> extends Queue<E>{
 
     @Override
     public E dequeue() {
-        if(isEmpty()) {
+        if(isEmpty())
             return null;
-        }
         E currentValue = start.data;
         start = start.next;
+        if(isEmpty())
+            end = null;
         return currentValue;
     }
 

module4/src/main/java/com/hithomelabs/princeton1/module4/LinkedStack.java

@@ -17,7 +17,6 @@ public class LinkedStack<E> extends Stack<E>{
     }
 
     Node<E> head = null;
-    Node<E> endPtr = null;
     int stackLength = 0;
 
     @Override
@@ -28,11 +27,8 @@ public class LinkedStack<E> extends Stack<E>{
     @Override
     public void push(E element) {
         Node<E> new_node = new Node<E>(element);
-        if(stackLength == 0)
-            head = new_node;
-        else
-            endPtr.next = new_node;
-        endPtr = new_node;
+        new_node.next = head;
+        head = new_node;
         stackLength++;
     }
 
@@ -40,15 +36,8 @@ public class LinkedStack<E> extends Stack<E>{
     public E pop() {
         if(stackLength == 0)
             return null;
-        if(stackLength == 1)
-            head = null;
-        Node<E> secondLastPtr = head;
-        while(secondLastPtr!=null && secondLastPtr.next != endPtr && secondLastPtr.next!=null)
-            secondLastPtr = secondLastPtr.next;
-        E currentValue = endPtr.data;
-        endPtr.next = null;
-        endPtr = secondLastPtr;
-        stackLength--;
+        E currentValue = head.data;
+        head = head.next;
         return currentValue;
     }
 

module5/src/main/java/com/hithomelabs/princeton1/module5/Shell.java

@@ -25,14 +25,23 @@ public class Shell<E> extends AbstractCustomSorts<E> {
     @Override
     public void sort(E[] arr) {
         MetaData metaData = new MetaData();
-        for(int i=arr.length/10; i>=0; i--){
-            hsort(arr, 3*i+1, metaData);
+
+        int h = 1;
+        while(3*h + 1 < arr.length){
+            h = 3*h + 1;
         }
+        while(h>=1){
+            hsort(arr, h, metaData);
+            h= h/3;
+        }
+//        for(int i=arr.length/10; i>=0; i--){
+//            hsort(arr, 3*i+1, metaData);
+//        }
         System.out.println("Array sorted (shell sort) with " + metaData.compares + " compares and " + metaData.swaps + " swaps");
     }
 
     private void hsort(E[] arr, int h, MetaData metadata) {
-        for(int i=0; i<arr.length; i=i+h){
+        for(int i=h; i<arr.length; i=i+1){
             int k = i;
             for(int j=i-h; j>=0; j=j-h){
                 metadata.compares++;

module6/src/main/java/com/hithomelabs/princeton1/module6/Merge.java

@@ -5,8 +5,11 @@ import com.hithomelabs.princeton1.module5.AbstractCustomSorts;
 import java.util.Arrays;
 
 public class Merge<E> extends AbstractCustomSorts<E> {
+    private E[] auxArr;
+
     @Override
     public void sort(E[] arr) {
+        auxArr = (E[]) new Object[arr.length];
         merge_sort(arr, 0, arr.length-1);
     }
 
@@ -17,21 +20,18 @@ public class Merge<E> extends AbstractCustomSorts<E> {
             merge_sort(arr, mid_index + 1, high_index);
 
             // Copy array
-            E[] auxArr = (E[]) new Object[high_index - low_index + 1];
-            int index = 0;
             for(int i=low_index; i<= high_index; i++)
-                auxArr[index++] = arr[i];
+                auxArr[i] = arr[i];
 
             // Sort
-            int low_index_ptr = 0;
-            int mid_index_ptr = (auxArr.length - 1)/2;
+            int low_index_ptr = low_index;
+            int mid_index_ptr = low_index + (high_index - low_index)/2;
             int high_index_ptr = mid_index_ptr + 1;
             if(!less((Comparable<E>) auxArr[mid_index_ptr], auxArr[high_index_ptr])) {
                 for (int i = low_index; i <= high_index; i++) {
                     if (low_index_ptr > mid_index_ptr) {
-                        arr[i] = auxArr[high_index_ptr];
-                        high_index_ptr++;
-                    } else if (high_index_ptr >= auxArr.length)
+                        arr[i] = auxArr[high_index_ptr++];
+                    } else if (high_index_ptr > high_index)
                         arr[i] = auxArr[low_index_ptr++];
                     else if (less((Comparable<E>) auxArr[low_index_ptr], auxArr[high_index_ptr]))
                         arr[i] = auxArr[low_index_ptr++];

module7/src/main/java/com/hithomelabs/princeton1/module7/Quick.java

@@ -34,23 +34,17 @@ public class Quick<E> extends AbstractCustomSorts<E> {
             while (i<=high && !less((Comparable<E>) arr[low], arr[i]))
                 i++;
             // Find the j index less than 1st element
-            while (!less((Comparable<E>) arr[j], arr[low]) && j > low)
+            while (less((Comparable<E>) arr[low], arr[j]) && j > low)
                 j--;
             // Break if indexes are crossed
-            if(j <= i)
+            if(j < i)
                 break;
             // Swap index values of i & j
             if(less((Comparable<E>) arr[j], arr[i]))
-                exch(arr, i++, j--);
+                exch(arr, i, j);
         }
         // Swap 1st element to it's correct position
-        int k_index = low+1;
-        while (k_index <= high){
-            if(less((Comparable<E>) arr[low], arr[k_index]))
-                break;
-            k_index++;
-        }
-        exch(arr, low, k_index-1);
-        return k_index - 1;
+        exch(arr, low, j);
+        return j;
     }
 }