Zadatak 1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Vezba_03_2017
{
     class StackA
    {
        private int[] _items;
        private int _count;

        public StackA()
        {
            _items = new int[5];
            _count = 0;
        }

        public bool IsEmpty
        {
            get { return _count == 0; }
        }

        public void Push(int x)
        {
            if (_count == _items.Length)
            {
                int[] newItems = new int[_items.Length * 2];
                for (int i = 0; i < _items.Length; i++)
                    newItems[i] = _items[i];
                _items = newItems;
            }

            _items[_count] = x;
            _count++;
        }

        public int Pop()
        {
            if (_count == 0)
                throw new InvalidOperationException("The stack is empty.");

            if (_count <= _items.Length / 4)
            {
                int[] newItems = new int[_items.Length / 2];
                for (int i = 0; i < newItems.Length; i++)
                    newItems[i] = _items[i];
                _items = newItems;
            }

            _count--;
            return _items[_count];

        }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();

            for (int i = _count - 1; i >= 0; i--)
            {
                sb.AppendFormat("{0} ", _items[i]);
            }

            return sb.ToString();
        }

    }
}