ReverseStack.cs

using System;
using System.Collections.Generic;

namespace Algorithms.Stack
{
    /// <summary>
    ///     Reverses the elements in a stack using recursion.
    /// @author Mohit Singh. <a href="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/mohit-gogitter">mohit-gogitter</a>
    /// </summary>
    public class ReverseStack
    {
        /// <summary>
        /// Recursively reverses the elements of the specified stack.
        /// </summary>
        /// <typeparam name="T">The type of elements in the stack.</typeparam>
        /// <param name="stack">The stack to be reversed. This parameter cannot be null.</param>
        /// <exception cref="ArgumentNullException">Thrown when the stack parameter is null.</exception>
        public void Reverse<T>(Stack<T> stack)
        {
            if (stack.Count == 0)
            {
                return;
            }

            T temp = stack.Pop();
            Reverse(stack);
            InsertAtBottom(stack, temp);
        }

        private void InsertAtBottom<T>(Stack<T> stack, T value)
        {
            if (stack.Count == 0)
            {
                stack.Push(value);
            }
            else
            {
                T temp = stack.Pop();
                InsertAtBottom(stack, value);
                stack.Push(temp);
            }
        }
    }
}