Done with Precourse 1

Exercise_1.java

@@ -8,28 +8,47 @@ class Stack {
     boolean isEmpty() 
     { 
         //Write your code here 
+        return (top == -1);
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        this.top = -1;
     } 
 
     boolean push(int x) 
     { 
         //Check for stack Overflow
         //Write your code here
+        if (top == MAX - 1) {
+            System.out.println("Stack Overflow! Cannot push " + x);
+            return false;
+        }
+        a[++top] = x;
+        System.out.println("Pushed: " + x);
+        return true;
     } 
 
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
         //Write your code here
+        if (isEmpty()) {
+            System.out.println("Stack Underflow! Stack is empty.");
+            return -1;
+        }
+        return a[top--];
     } 
 
     int peek() 
     { 
         //Write your code here
+        if (isEmpty()) {
+            System.out.println("Stack is empty.");
+            return -1;
+        }
+        return a[top];
     } 
 } 
 

Exercise_3.java → LinkedList.java

@@ -1,70 +1,89 @@
-import java.io.*; 
-
-// Java program to implement 
-// a Singly Linked List 
-public class LinkedList { 
-
-    Node head; // head of list 
-
-    // Linked list Node. 
-    // This inner class is made static 
-    // so that main() can access it 
-    static class Node { 
-
-        int data; 
-        Node next; 
-
-        // Constructor 
-        Node(int d) 
-        { 
-            //Write your code here 
-        } 
-    } 
-
-    // Method to insert a new node 
-    public static LinkedList insert(LinkedList list, int data) 
-    { 
-        // Create a new node with given data 
-
-        // If the Linked List is empty, 
-        // then make the new node as head 
-
-            // Else traverse till the last node 
-            // and insert the new_node there 
-
-            // Insert the new_node at last node 
-        // Return the list by head 
-
-    } 
-
-    // Method to print the LinkedList. 
-    public static void printList(LinkedList list) 
-    {  
-        // Traverse through the LinkedList 
-
-            // Print the data at current node 
-
-            // Go to next node 
-    } 
-
-    // Driver code 
-    public static void main(String[] args) 
-    { 
-        /* Start with the empty list. */
-        LinkedList list = new LinkedList(); 
-
-        // 
-        // ******INSERTION****** 
-        // 
-
-        // Insert the values 
-        list = insert(list, 1); 
-        list = insert(list, 2); 
-        list = insert(list, 3); 
-        list = insert(list, 4); 
-        list = insert(list, 5); 
-
-        // Print the LinkedList 
-        printList(list); 
-    } 
+import java.io.*; 
+
+// Java program to implement 
+// a Singly Linked List 
+public class LinkedList { 
+
+    Node head; // head of list 
+
+    // Linked list Node. 
+    // This inner class is made static 
+    // so that main() can access it 
+    static class Node { 
+
+        int data; 
+        Node next; 
+
+        // Constructor 
+        Node(int d) 
+        { 
+            //Write your code here 
+            data = d;
+            next = null;
+        } 
+    } 
+
+    // Method to insert a new node 
+    public static LinkedList insert(LinkedList list, int data) 
+    { 
+        // Create a new node with given data 
+        Node new_node = new Node(data); 
+        new_node.next = null;
+
+        // If the Linked List is empty, 
+        // then make the new node as head 
+        if (list.head == null) { 
+            list.head = new_node; 
+        } 
+        else { 
+            // Else traverse till the last node 
+            // and insert the new_node there 
+            Node last = list.head; 
+            while (last.next != null) { 
+                last = last.next; 
+            } 
+
+            // Insert the new_node at last node 
+            last.next = new_node; 
+        } 
+
+        // Return the list by head 
+        return list;        
+    } 
+
+    // Method to print the LinkedList. 
+    public static void printList(LinkedList list) 
+    {  
+        // Traverse through the LinkedList 
+        Node currNode = list.head; 
+
+        while (currNode != null) { 
+            // Print the data at current node 
+            System.out.print(currNode.data + " "); 
+
+            // Go to next node 
+            currNode = currNode.next; 
+        } 
+    } 
+
+    // Driver code 
+    public static void main(String[] args) 
+    { 
+        /* Start with the empty list. */
+        LinkedList list = new LinkedList(); 
+
+        // 
+        // ******INSERTION****** 
+        // 
+
+        // Insert the values 
+        list = insert(list, 1); 
+        list = insert(list, 2); 
+        list = insert(list, 3); 
+        list = insert(list, 4); 
+        list = insert(list, 5); 
+
+        // Print the LinkedList 
+        printList(list); 
+    } 
 }

Exercise_2.java → StackAsLinkedList.java

@@ -1,52 +1,72 @@
-public class StackAsLinkedList { 
-
-    StackNode root; 
-
-    static class StackNode { 
-        int data; 
-        StackNode next; 
-
-        StackNode(int data) 
-        { 
-            //Constructor here 
-        } 
-    } 
-
-
-    public boolean isEmpty() 
-    { 
-        //Write your code here for the condition if stack is empty. 
-    } 
-
-    public void push(int data) 
-    { 
-        //Write code to push data to the stack. 
-    } 
-
-    public int pop() 
-    { 	
-	//If Stack Empty Return 0 and print "Stack Underflow"
-        //Write code to pop the topmost element of stack.
-	//Also return the popped element 
-    } 
-
-    public int peek() 
-    { 
-        //Write code to just return the topmost element without removing it.
-    } 
-
-	//Driver code
-    public static void main(String[] args) 
-    { 
-
-        StackAsLinkedList sll = new StackAsLinkedList(); 
-
-        sll.push(10); 
-        sll.push(20); 
-        sll.push(30); 
-
-        System.out.println(sll.pop() + " popped from stack"); 
-
-        System.out.println("Top element is " + sll.peek()); 
-    } 
-} 
+public class StackAsLinkedList { 
+
+    StackNode root; 
+
+    static class StackNode { 
+        int data; 
+        StackNode next; 
+
+        StackNode(int data) 
+        { 
+            //Constructor here 
+            this.data = data;
+            this.next = null;
+        } 
+    } 
+
+
+    public boolean isEmpty() 
+    { 
+        //Write your code here for the condition if stack is empty. 
+        return root == null;
+    } 
+
+    public void push(int data) 
+    { 
+        //Write code to push data to the stack. 
+        StackNode newNode = new StackNode(data);
+        newNode.next = root;
+        root = newNode;
+    } 
+
+    public int pop() 
+    { 	
+	//If Stack Empty Return 0 and print "Stack Underflow"
+        //Write code to pop the topmost element of stack.
+	//Also return the popped element 
+    if (isEmpty()) {
+            System.out.println("Stack Underflow");
+            return 0;
+        } else {
+            int popped = root.data;
+            root = root.next;
+            return popped;
+        }
+    } 
+
+    public int peek() 
+    { 
+        //Write code to just return the topmost element without removing it.
+        if (isEmpty()) {
+            System.out.println("Stack is Empty");
+            return 0;
+        } else {
+            return root.data;
+        }
+    } 
+
+	//Driver code
+    public static void main(String[] args) 
+    { 
+
+        StackAsLinkedList sll = new StackAsLinkedList(); 
+
+        sll.push(10); 
+        sll.push(20); 
+        sll.push(30); 
+
+        System.out.println(sll.pop() + " popped from stack"); 
+
+        System.out.println("Top element is " + sll.peek()); 
+    } 
+}