Precourse1-Exercise1

Exercise_1.java

@@ -1,35 +1,59 @@
-class Stack { 
-    //Please read sample.java file before starting.
-  //Kindly include Time and Space complexity at top of each file
+class Stack {
+
+    // Time Complexity:
+// push() - O(1)
+// pop()  - O(1)
+// peek() - O(1)
+// isEmpty() - O(1)
+
+// Space Complexity: O(MAX)
+
     static final int MAX = 1000; 
     int top; 
     int a[] = new int[MAX]; // Maximum size of Stack 
 
     boolean isEmpty() 
-    { 
-        //Write your code here 
+    {
+        return top == -1;
     } 
 
     Stack() 
     { 
-        //Initialize your constructor 
+        top = -1;
     } 
 
     boolean push(int x) 
     { 
-        //Check for stack Overflow
-        //Write your code here
+        if(top >=MAX-1) {
+            return false;
+        }
+        else{
+            a[++top] = x;
+            return true;
+        }
+
+
     } 
 
     int pop() 
-    { 
-        //If empty return 0 and print " Stack Underflow"
-        //Write your code here
+    {
+        if(isEmpty())
+        {
+            System.out.println("Stack Underflow");
+            return 0;
+        }
+        else
+        {
+            return a[top--];
+        }
     } 
 
     int peek() 
     { 
-        //Write your code here
+        if(isEmpty())
+            return 0;
+        else
+            return a[top];
     } 
 } 
 
@@ -40,7 +64,7 @@ public static void main(String args[])
         Stack s = new Stack(); 
         s.push(10); 
         s.push(20); 
-        s.push(30); 
+        s.push(30);
         System.out.println(s.pop() + " Popped from stack"); 
     } 
 }