Completed PreCourse-1

Exercise_1.cpp

@@ -1,54 +1,101 @@
-#include <bits/stdc++.h> 
-
-using namespace std; 
-
-#define MAX 1000 
-
-class Stack {
-  //Please read sample.java file before starting.
-  //Kindly include Time and Space complexity at top of each file
-    int top; 
-
-public: 
-    int a[MAX]; // Maximum size of Stack 
-
-    Stack() { //Constructor here } 
-    bool push(int x); 
-    int pop(); 
-    int peek(); 
-    bool isEmpty(); 
-}; 
-
-bool Stack::push(int x) 
-{ 
-    //Your code here
-    //Check Stack overflow as well
-} 
-
-int Stack::pop() 
-{ 
-    //Your code here
-    //Check Stack Underflow as well 
-} 
-int Stack::peek() 
-{ 
-    //Your code here
-    //Check empty condition too
-} 
-
-bool Stack::isEmpty() 
-{ 
-    //Your code here 
-} 
-
-// Driver program to test above functions 
-int main() 
-{ 
-    class Stack s; 
-    s.push(10); 
-    s.push(20); 
-    s.push(30); 
-    cout << s.pop() << " Popped from stack\n"; 
-
-    return 0; 
-} 
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define MAX 1000
+
+/*
+Time Complexity :
+    push(): O(1)
+    pop(): O(1)
+    peek(): O(1)
+    isEmpty(): O(1)
+
+Space Complexity :
+    stack: O(n), n is number of elements in stack
+
+Did this code successfully run on Leetcode : Couldn't find the leetcode problem
+
+Any problem you faced while coding this : None
+*/
+class Stack
+{
+    int top;
+
+public:
+    int a[MAX]; // Maximum size of Stack
+
+    Stack()
+    {
+        top = -1;
+    }
+    bool push(int x);
+    int pop();
+    int peek();
+    bool isEmpty();
+};
+
+// Push data onto the stack
+bool Stack::push(int x)
+{
+    if (top >= MAX)
+    {
+        return false;
+    }
+
+    a[++top] = x;
+
+    return true;
+}
+
+// Pop data from the stack
+int Stack::pop()
+{
+    if (isEmpty())
+    {
+        return -1;
+    }
+    else
+    {
+        return a[top--];
+    }
+}
+
+// Peek the top element of the stack
+int Stack::peek()
+{
+    if (isEmpty())
+    {
+        return -1;
+    }
+
+    return a[top];
+}
+
+// Check if the stack is empty
+bool Stack::isEmpty()
+{
+    if (top < 0)
+    {
+        return true;
+    }
+
+    return false;
+}
+
+// Driver program to test above functions
+int main()
+{
+    class Stack s;
+    s.push(10);
+    s.push(20);
+    s.push(30);
+    cout << s.peek() << " Peeked from stack\n";
+    cout << s.pop() << " Popped from stack\n";
+    cout << s.peek() << " Peeked from stack\n";
+    cout << s.pop() << " Popped from stack\n";
+    cout << s.peek() << " Peeked from stack\n";
+    cout << s.pop() << " Popped from stack\n";
+
+    return 0;
+}

Exercise_2.cpp

@@ -1,52 +1,100 @@
-#include <bits/stdc++.h> 
-using namespace std; 
-
-// A structure to represent a stack 
-class StackNode { 
-public: 
-    int data; 
-    StackNode* next; 
-}; 
-
-StackNode* newNode(int data) 
-{ 
-    StackNode* stackNode = new StackNode(); 
-    stackNode->data = data; 
-    stackNode->next = NULL; 
-    return stackNode; 
-} 
-
-int isEmpty(StackNode* root) 
-{ 
-    //Your code here 
-} 
-
-void push(StackNode** root, int data) 
-{ 
-    //Your code here 
-} 
-
-int pop(StackNode** root) 
-{ 
-    //Your code here 
-} 
-
-int peek(StackNode* root) 
-{ 
-    //Your code here 
-} 
-
-int main() 
-{ 
-    StackNode* root = NULL; 
-
-    push(&root, 10); 
-    push(&root, 20); 
-    push(&root, 30); 
-
-    cout << pop(&root) << " popped from stack\n"; 
-
-    cout << "Top element is " << peek(root) << endl; 
-
-    return 0; 
-} 
+#include <bits/stdc++.h>
+using namespace std;
+
+/*
+Time Complexity :
+    push(): O(1)
+    pop(): O(1)
+    peek(): O(1)
+    isEmpty(): O(1)
+
+Space Complexity :
+    stack: O(n), n is number of elements in the stack
+
+Did this code successfully run on Leetcode : Couldn't find the leetcode problem
+
+Any problem you faced while coding this : None
+*/
+
+// A structure to represent a stack
+class StackNode
+{
+public:
+    int data;
+    StackNode *next;
+};
+
+StackNode *newNode(int data)
+{
+    StackNode *stackNode = new StackNode();
+    stackNode->data = data;
+    stackNode->next = NULL;
+    return stackNode;
+}
+
+// Check if the stack is empty
+int isEmpty(StackNode *root)
+{
+    return root == NULL;
+}
+
+// Push data onto the stack
+void push(StackNode **root, int data)
+{
+    StackNode *node = newNode(data);
+
+    node->next = *root;
+
+    *root = node;
+}
+
+// Pop data from the stack
+int pop(StackNode **root)
+{
+    if (isEmpty(*root))
+    {
+        return -1;
+    }
+
+    StackNode *node = *root;
+
+    *root = (*root)->next;
+
+    int popped = node->data;
+
+    delete node; // Free memory to prevent memory leaks
+
+    return popped;
+}
+
+// Peek the top element of the stack
+int peek(StackNode *root)
+{
+    if (isEmpty(root))
+    {
+        return -1;
+    }
+
+    return root->data;
+}
+
+int main()
+{
+    StackNode *root = NULL;
+
+    push(&root, 10);
+    push(&root, 20);
+    push(&root, 30);
+
+    cout << pop(&root) << " popped from stack\n";
+
+    cout << "Top element is " << peek(root) << endl;
+
+    cout << pop(&root) << " popped from stack\n";
+
+    cout << "Top element is " << peek(root) << endl;
+
+    cout << pop(&root) << " popped from stack\n";
+
+    return 0;
+}