Reddit Daily Programmer 298 Easy

Easy.cs

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

namespace Reddit
{
    internal static class Easy
    {
        internal static string Run(string input)
        {
            var collection = new LinkedList<char>(input);

            Rule2(collection);
            Rule1(collection);

            var builder = new StringBuilder();
            foreach (char value in collection)
            {
                builder.Append(value);
            }

            return builder.Length == 0 ? null : builder.ToString();
        }

        internal class Pair
        {
            internal LinkedListNode<char> Left;
            internal LinkedListNode<char> Right;
        }

        internal static List<Pair> Parse(LinkedList<char> collection)
        {
            var items = new List<Pair>();

            var stack = new Stack<LinkedListNode<char>>();

            var current = collection.First;
            while (current != null)
            {
                char c = current.Value;
                if (c == '(')
                {
                    stack.Push(current);
                }
                else
                {
                    if (c == ')')
                    {
                        if (stack.Count > 0)
                        {
                            var previous = stack.Pop();

                            var item = new Pair();
                            item.Left = previous;
                            item.Right = current;

                            items.Add(item);
                        }
                    }
                }

                current = current.Next;
            }

            return items;
        }

        internal static void Rule1(LinkedList<char> collection)
        {
            var items = Parse(collection);
            foreach (var item in items)
            {
                var left = item.Left;
                var right = item.Right;

                if (items.Any(e => 
                    e.Left.Previous == left &&
                    e.Right.Next == right))
                {
                    collection.Remove(left);
                    collection.Remove(right);
                }
            }
        }

        internal static void Rule2(LinkedList<char> collection)
        {
            var items = Parse(collection);
            foreach (var item in items)
            {
                var left = item.Left;
                var right = item.Right;

                if (left.Next == right)
                {
                    collection.Remove(left);
                    collection.Remove(right);
                }
            }
        }
    }
}