From 225ff3422bb18e8ad930285148cc2c0a1e5aa7ce Mon Sep 17 00:00:00 2001
From: Abhinav <101085681+Abhinav-Sriharsha@users.noreply.github.com>
Date: Sat, 19 Oct 2024 21:06:02 -0700
Subject: [PATCH 1/2] Done PreCourse-1

---
 Exercise_1.java                           | 22 +++++++++++++++-
 Exercise_3.java => LinkedList.java        | 27 +++++++++++++++++--
 Exercise_2.java => StackAsLinkedList.java | 32 ++++++++++++++++++++++-
 3 files changed, 77 insertions(+), 4 deletions(-)
 rename Exercise_3.java => LinkedList.java (70%)
 rename Exercise_2.java => StackAsLinkedList.java (56%)

diff --git a/Exercise_1.java b/Exercise_1.java
index 314a3cb45..04f90606c 100644
--- a/Exercise_1.java
+++ b/Exercise_1.java
@@ -7,29 +7,49 @@ class Stack {
   
     boolean isEmpty() 
     { 
-        //Write your code here 
+        if(top==-1)
+            return true;
+        else
+            return false;
     } 
 
     Stack() 
     { 
         //Initialize your constructor 
+        top=-1;
     } 
   
     boolean push(int x) 
     { 
         //Check for stack Overflow
+        if(top>MAX-1)
+            return false;
+        else
+        {
+            top=top+1;
+            a[top]=x;
+            return true;
+        }
         //Write your code here
     } 
   
     int pop() 
     { 
         //If empty return 0 and print " Stack Underflow"
+        if(top==-1)
+        {
+            System.out.print("Stack Underflow");
+            return 0;
+        }
+        else
+            return a[top--];
         //Write your code here
     } 
   
     int peek() 
     { 
         //Write your code here
+        return top;
     } 
 } 
   
diff --git a/Exercise_3.java b/LinkedList.java
similarity index 70%
rename from Exercise_3.java
rename to LinkedList.java
index fb66d329d..5a192d405 100644
--- a/Exercise_3.java
+++ b/LinkedList.java
@@ -18,6 +18,9 @@ static class Node {
         Node(int d) 
         { 
             //Write your code here 
+            this.data =d;
+           
+
         } 
     } 
   
@@ -25,9 +28,24 @@ static class Node {
     public static LinkedList insert(LinkedList list, int data) 
     { 
         // Create a new node with given data 
+        Node newNode =new Node(data);
    
         // If the Linked List is empty, 
-        // then make the new node as head 
+        // then make the new node as head
+        if(list.head==null)
+        {
+            list.head=newNode;
+        }
+        else
+        {
+            Node temp =list.head;
+            while(temp.next!= null)
+            {
+                temp=temp.next;
+            }
+            temp.next=newNode;
+        } 
+        return list;
         
             // Else traverse till the last node 
             // and insert the new_node there 
@@ -41,7 +59,12 @@ public static LinkedList insert(LinkedList list, int data)
     public static void printList(LinkedList list) 
     {  
         // Traverse through the LinkedList 
-   
+        Node temp=list.head;
+        while(temp !=null)
+        {
+            System.out.println(temp.data+ " ");
+            temp=temp.next;
+        }
             // Print the data at current node 
        
             // Go to next node 
diff --git a/Exercise_2.java b/StackAsLinkedList.java
similarity index 56%
rename from Exercise_2.java
rename to StackAsLinkedList.java
index 5a9c4868c..9260cf213 100644
--- a/Exercise_2.java
+++ b/StackAsLinkedList.java
@@ -8,6 +8,8 @@ static class StackNode {
   
         StackNode(int data) 
         { 
+            this.data=data;
+            this.next=null;
             //Constructor here 
         } 
     } 
@@ -16,16 +18,42 @@ static class StackNode {
     public boolean isEmpty() 
     { 
         //Write your code here for the condition if stack is empty. 
+
+        if(root==null)
+            return true;
+        return false;
     } 
   
     public void push(int data) 
     { 
-        //Write code to push data to the stack. 
+        //Write code to push data to the stack.
+        StackNode newNode=new StackNode(data) ;
+        if(root==null)
+        {
+            root=newNode;
+            newNode.next=null;
+        }
+        else{
+            newNode.next=root;
+            root=newNode;
+        }
     } 
   
     public int pop() 
     { 	
 	//If Stack Empty Return 0 and print "Stack Underflow"
+        if(root==null)
+        {
+            System.out.println("Stack Underflow");
+            return 0;
+        }
+        else{
+            StackNode temp =root;
+            int x=temp.data;
+            root=temp.next;
+            temp=null;
+            return x;
+        }
         //Write code to pop the topmost element of stack.
 	//Also return the popped element 
     } 
@@ -33,6 +61,8 @@ public int pop()
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        StackNode temp= root;
+        return temp.data;
     } 
   
 	//Driver code

From 6248bf0de67125f13b3ade9a9d653ba682d05da0 Mon Sep 17 00:00:00 2001
From: Abhinav <101085681+Abhinav-Sriharsha@users.noreply.github.com>
Date: Tue, 22 Oct 2024 21:08:46 -0700
Subject: [PATCH 2/2] Made changes to peek method

---
 Exercise_1.java        | 12 +++++++++++-
 StackAsLinkedList.java |  8 ++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Exercise_1.java b/Exercise_1.java
index 04f90606c..ace79ccca 100644
--- a/Exercise_1.java
+++ b/Exercise_1.java
@@ -1,3 +1,6 @@
+// Time complexity O(1) for each operation
+// Problems faced: Unable to calculate the time and spce complexity properly
+
 class Stack { 
     //Please read sample.java file before starting.
   //Kindly include Time and Space complexity at top of each file
@@ -49,7 +52,13 @@ int pop()
     int peek() 
     { 
         //Write your code here
-        return top;
+        if(top==-1)
+        {
+            System.out.println("Stack is empty");
+            return 0;
+        }
+        else
+            return a[top];
     } 
 } 
   
@@ -62,5 +71,6 @@ public static void main(String args[])
         s.push(20); 
         s.push(30); 
         System.out.println(s.pop() + " Popped from stack"); 
+        
     } 
 }
diff --git a/StackAsLinkedList.java b/StackAsLinkedList.java
index 9260cf213..50112597b 100644
--- a/StackAsLinkedList.java
+++ b/StackAsLinkedList.java
@@ -61,8 +61,16 @@ public int pop()
     public int peek() 
     { 
         //Write code to just return the topmost element without removing it.
+        if(root==null)
+        {
+            System.out.println("Stack is empty");
+            return 0;
+        }
+        else
+        {
         StackNode temp= root;
         return temp.data;
+        }
     } 
   
 	//Driver code