public static class BracketsChecker {

    public class BracketErrorException : ApplicationException {

        public BracketErrorException(string message)
        : base(message) {
        }

    }

    public class BracketMismatchException : BracketErrorException {

        public readonly char openChar;
        public readonly char closeChar;
        public readonly int closePosition;

        public BracketMismatchException(char openChar, char closeChar, int closePosition)
        : base(string.Format("Bracket mismatch at {2}: got \"{1}\" for opening \"{0}\"", openChar, closeChar, closePosition)) {
            this.openChar = openChar;
            this.closeChar = closeChar;
            this.closePosition = closePosition;
        }

    }

    public class ExtraOpeningBracketException : BracketErrorException {

        public ExtraOpeningBracketException()
        : base("Extra opening bracket") {
        }

    }

    public class ExtraClosingBracketException : BracketErrorException {

        public readonly char closeChar;
        public readonly int closePosition;

        public ExtraClosingBracketException(char closeChar, int closePosition)
        : base(string.Format("Extra closing bracket at {1}: \"{0}\"", closeChar, closePosition)) {
            this.closeChar = closeChar;
            this.closePosition = closePosition;
        }

    }

    private class Bracket {

        char[] openChars;
        char[] closeChars;

        public Bracket(char[] openChars, char[] closeChars) {
            this.openChars = openChars;
            this.closeChars = closeChars;
        }

    }

    private static readonly Bracket[] Brackets = new[] {
        new Bracket(new[] { '(' }, new[] { ')' }),
        new Bracket(new[] { '[' }, new[] { ']' }),
        new Bracket(new[] { '{' }, new[] { '}' }),
    }

    private static readonly Dictionary<char, Bracket> BracketsByOpenChar =
        (
            from bracket in Brackets
            from openChar in bracket.openChars
            select new KeyValuePair<char, Bracket>(openChar, bracket)
        ).ToDictionary();

    private static readonly HashSet<char> CloseChars =
        new HashSet<char>(
            from bracket in Brackets
            from closeChar in bracket.CloseChars
            select closeChar
        );

    public static void CheckString(string str) {
        Stack<Bracket> currentState = new Stack<Bracket>();
        for(int i=0; i<str.length; i++) {
            if(BracketsByOpenChar.ContainsKey(str[i])) {
                currentState.Push(BracketsByOpenChar[str[i]]);
            } else if(CloseChars.Contains(str[i])) {
                if(currentState.IsEmpty) {
                    throw new ExtraClosingBracketException();
                }
                if(!currentState.Peek().closeChars.Contains(str[i])) {
                    throw new BracketsMismatchException();
                }
                currentState.Pop();
            }
        }
        if(!currentState.IsEmpty) {
            throw new ExtraOpeningBracketException();
        }
    }

}