Monobilliards

using System;
using System.Collections.Generic;

namespace Monobilliards
{
    public class Monobilliards : IMonobilliards
    {
        public bool IsCheater(IList<int> inspectedBalls)
        {
            var stack = new Stack<int>();

            var maxBalls = 0;

            for (int i = 0; i < inspectedBalls.Count - 1; i++)
            {
                if (inspectedBalls[i] > maxBalls)
                {
                    for (int j = maxBalls + 1; j < inspectedBalls[i] + 1; j++)
                        stack.Push(j);
                }

                var last = stack.Peek();
                if (last == inspectedBalls[i])
                {
                    if (stack.Pop() > maxBalls)
                        maxBalls = last;
                }
                else if (last > inspectedBalls[i])
                {
                    return true;
                }
            }
            return false;
        }
    }
}