Question

Write a method to reverse the order of elements on stack S using two additional stacks. When the method completes, stack S should have the items it originally had, but in reversed order.

Answer 1

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import java.util.*;

public class StackOp {
    private static Stack reverse(Stack stack) {
        // This function is used to reverse the stack using another two stacks First we will copy the elements of the
        // stack to s1 and then s1 to s2 then s2 to stack Then the stack elements will be reversed
        Stack<Integer> s1 = new Stack<Integer>();// Creating objects for stacks
        Stack<Integer> s2 = new Stack<Integer>();
        int temp;
        while (!stack.empty())s1.push((int) stack.pop());// Moving elements from stack to s1
        while (!s1.empty())s2.push((int) s1.pop());// Moving elements from s1 to s2
        while (!s2.empty())stack.push(s2.pop()); // Moving elements from s2 to stack
        return stack; // Returning stack
    }

    public static void main(String args[]) {
        //This is the driver method for this program here we are creating the stack object and inserting the elements to
        // it and then we are calling stack reverse function then displaying the result
        Scanner in = new Scanner(System.in);
        Stack<Integer> stack = new Stack<Integer>();
        int ch = 0;
        while (true) {
            System.out.println("1-enter\n2-exit");// Taking the input from the user and storing it in the stack
            ch = in.nextInt();
            if (ch == 1) {
                System.out.println("Enter data:");
                stack.push(in.nextInt());
            } else if (ch == 2) {
                break;
            } else {
                System.out.println("Choose the option correctly");
            }
        }
        System.out.println("Before Reverse Stack elements");
        System.out.println(stack);
        stack = reverse(stack);
        System.out.println("After Reverse Stack elements");
        System.out.println(stack);
    }
}

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