Merge pull request #10 from yash-b98/patch-2

Stack List Implementation

Author: dynamitechetan

data_structures/Stacks.java

@@ -38,20 +38,81 @@ public void makeEmpty(){ //Doesn't delete elements in the array but if you call
 		top = -1;			 //push method after calling makeEmpty it will overwrite previous values
 	}
 }
+
+
+/* This is ArrayList Implementation of stack , Where size is not
+ 	a problem we can extend the stack as much as we want*/ 
+class Stack2{
+		
+		
+		ArrayList<Integer> stackList;
+		
+		Stack2(){ //constructor
+			stackList=new ArrayList<>();
+		}
+		
+		
+		void push(int value){ //adds value to the end of list which is the top for stack
+			stackList.add(value);
+		}
+		
+		int pop(){ //pops last element of list which is indeed the top for Stack 
+			
+			if(!isEmpty()){ // checks for an empty Stack
+				
+				int popValue=stackList.get(stackList.size()-1);
+				stackList.remove(stackList.size()-1);  //removes the poped element from the list
+				return popValue;
+			}
+			else{
+				System.out.print("The stack is already empty  ");
+				return -1;
+			}
+			
+		}
+		
+		boolean isEmpty(){ //checks for empty Stack
+			if(stackList.isEmpty())
+				return true;
+			
+			else return false;
+			
+		}
+		
+		int peek(){ //top element of stack
+			return stackList.get(stackList.size()-1);
+		}
+	}
+
 //Example
 public class Stacks{
 	public static void main(String args[]){
-		Stack myStack = new Stack(4); //Declare a stack of maximum size 4
-		//Populate the stack
-		myStack.push(5);
-		myStack.push(8);
-		myStack.push(2);
-		myStack.push(9);
-
-		System.out.println(myStack.isEmpty()); //will print false
-		System.out.println(myStack.isFull()); //will print true
-		System.out.println(myStack.peek()); //will print 9
-		System.out.println(myStack.pop()); //will print 9
-		System.out.println(myStack.peek()); // will print 2
-	}
-}
+			Stack myStack = new Stack(4); //Declare a stack of maximum size 4
+ 		//Populate the stack
+ 		myStack.push(5);
+ 		myStack.push(8);
+  		myStack.push(2);
+  		myStack.push(9);
+  
+		System.out.println("*********************Stack Array Implementation*********************");
+  		System.out.println(myStack.isEmpty()); //will print false
+  		System.out.println(myStack.isFull()); //will print true
+  		System.out.println(myStack.peek()); //will print 9
+  		System.out.println(myStack.pop()); //will print 9
+  		System.out.println(myStack.peek()); // will print 2
+		
+		Stack2 myStack2 = new Stack2(); //Declare a stack of maximum size 4
+  		//Populate the stack
+ 		myStack2.push(5);
+		myStack2.push(8);
+ 		myStack2.push(2);
+ 		myStack2.push(9);
+ 
+ 		System.out.println("*********************Stack List Implementation*********************");
+ 		System.out.println(myStack2.isEmpty()); //will print false
+ 		System.out.println(myStack2.peek()); //will print 9
+ 		System.out.println(myStack2.pop()); //will print 9
+ 		System.out.println(myStack2.peek()); // will print 2
+ 		System.out.println(myStack2.pop()); //will print 2
+	}
+}