precourse 1 Done

Exercise_1.java

@@ -1,35 +1,75 @@
-class Stack { 
+// Time Complexity : O(1) for push(), pop(), peek(), and isEmpty()
+// Space Complexity : O(n) for storing n elements in the stack
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this : None
+
+
+// Your code here along with comments explaining your approach
+
+class Stack {
     //Please read sample.java file before starting.
   //Kindly include Time and Space complexity at top of each file
     static final int MAX = 1000; 
     int top; 
     int a[] = new int[MAX]; // Maximum size of Stack 
 
     boolean isEmpty() 
-    { 
-        //Write your code here 
+    {
+//        return true if stack is empty
+        if(top == -1){
+            return true;
+        } else {
+            return false;
+        }
     } 
 
     Stack() 
     { 
-        //Initialize your constructor 
-    } 
-
+        //Initialize your constructor
+        top = -1;
+    }
+
     boolean push(int x) 
-    { 
+    {
+//        insert an element on top of stack
         //Check for stack Overflow
         //Write your code here
+        if (top == MAX-1) {
+            System.out.println("Stack Overflow");
+            return false;
+        } else {
+            top++;
+            a[top] = x;
+            return true;
+        }
     } 
 
     int pop() 
-    { 
+    {
+//        pop the topmost element of stack
         //If empty return 0 and print " Stack Underflow"
         //Write your code here
+        if (top == -1) {
+            System.out.println("Stack Underflow");
+            return 0;
+        } else {
+            int ele = a[top];
+            top--;
+            return ele;
+        }
+
+
     } 
 
     int peek() 
-    { 
+    {
+//        return the topmost element of stack
         //Write your code here
+        if (top == -1) {
+            return 0;
+        } else {
+            return a[top];
+        }
     } 
 } 
 

LinkedList.java

@@ -0,0 +1,88 @@
+// Time Complexity : insert() -> O(1), printList() -> O(n)
+// Space Complexity : O(n)
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this : No
+
+// Your code here along with comments explaining your approach
+
+import java.io.*;
+
+// Java program to implement 
+// a Singly Linked List 
+public class LinkedList { 
+
+    Node head;// head of list
+    Node tail;//tail 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) 
+        {
+            this.data = 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
+        Node node = new Node(data);
+
+        // If the Linked List is empty, 
+        // then make the new node as head
+        // Else append the new node at the end and update tail
+        if (list.head == null) {
+            list.head = node;
+            list.tail = node;
+            return list;
+        } else {
+            list.tail.next = node;
+            list.tail = node;
+            return list;
+        }
+
+
+    } 
+
+    // Method to print the LinkedList. 
+    public static void printList(LinkedList list) 
+    {
+//        assign head to a temp node
+//        print data of each node until temp is null
+        Node temp = list.head;
+        while (temp!= null) {
+            System.out.println(temp.data);
+            temp = temp.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); 
+    } 
+}

PreCourse-1.iml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>