using System.Collections.Generic;
namespace BracketSet
{
    public enum BracketType
    {
        Open = 1,
        Closed = 2
    }

    public class BracketPair
    {
        public Bracket brkt_Open { get; private set; }
        public Bracket brkt_Close { get; private set; }

        public class Bracket
        {
            public BracketPair brktp_Owner { get; private set; }
            public char char_Bracket { get; private set; }
            public BracketType Type { get; private set; }

            public Bracket(BracketPair brktp_owner, char char_bracket, BracketType type)
            {
                this.brktp_Owner = brktp_owner;
                this.char_Bracket = char_bracket;
                this.Type = type;
            }
        }

        public BracketPair(char char_open, char char_close)
        {
            this.brkt_Open = new Bracket(this, char_open, BracketType.Open);
            this.brkt_Close = new Bracket(this, char_close, BracketType.Closed);
        }
    }

    public class BracketPairCollection : List<BracketPair>
    {
        public void Add(char char_open, char char_close)
        {
            this.Add(new BracketPair(char_open, char_close));
        }
        public bool IsValid(string str_val)
        {
            List<BracketSet.BracketPair.Bracket> brkt_lst_brackets = new List<BracketSet.BracketPair.Bracket>();

            foreach (char char_ in str_val)
            {
                foreach (BracketPair pair in this)
                {
                    BracketSet.BracketPair.Bracket brkt;
                    if (char_ == (brkt = pair.brkt_Open).char_Bracket || char_ == (brkt = pair.brkt_Close).char_Bracket)
                    {
                        brkt_lst_brackets.Add(brkt);
                        break;
                    }
                }
            }

            if (brkt_lst_brackets.Count == 0 ||
                brkt_lst_brackets.Count % 2 == 1 ||
                brkt_lst_brackets[0].Type == BracketType.Closed ||
                brkt_lst_brackets[brkt_lst_brackets.Count - 1].Type == BracketType.Open)
            {
                return false;
            }

            int int_LastIndex = -1;
            while (brkt_lst_brackets.Count > 0)
            {
                int int_closingIndex = brkt_lst_brackets.FindIndex(o => o.Type == BracketType.Closed);
                if (int_closingIndex == int_LastIndex)
                {
                    return false;
                }

                int int_openingIndex = int_closingIndex - 1;

                if (int_openingIndex < 0 || int_closingIndex < 0)
                {
                    return false;
                }

                if (brkt_lst_brackets[int_openingIndex].brktp_Owner == brkt_lst_brackets[int_closingIndex].brktp_Owner)
                {
                    brkt_lst_brackets.RemoveAt(int_closingIndex);
                    brkt_lst_brackets.RemoveAt(int_openingIndex);
                }
            }

            return true;
        }
    }
}