Balance Parentheses in a string

balance.cs

// netcoreapp3.1

using System;
using System.Diagnostics;
using System.Linq;
using System.Text.RegularExpressions;

namespace Jerry
{
    class Program
    {
        private static readonly Regex _regex = new Regex(_pattern);
        private static readonly Stopwatch _stopwatch = new Stopwatch();
        private static readonly Random _random = new Random((int)DateTime.Now.Ticks);
        private const string _pattern = @"\((?>\((?<parens>)|[^()]+|\)(?<-parens>))*(?(parens)(?!))\)";

        static void Main(string[] args)
        {
            Do(10);
            Do(10);
            Do(10);
            Do(20);
            Do(30);

            void Do(int size)
            {
                // create random (()()() string and append invalid text at the end.
                var input = string.Join(string.Empty, Enumerable.Range(1, size).Select(x => (char)_random.Next(40, 42))) + "JerryNixon";

                // start measuring
                _stopwatch.Restart();

                // look for pattern match in the string, return all found
                var output = string.Join(string.Empty, _regex.Matches(input).Select(x => x.Value));

                // stop measuring
                _stopwatch.Stop();

                // output
                Console.WriteLine($"\r\nSize: {size}\r\nInput: {input}\r\nOutput: {output}\r\nTime: {_stopwatch.Elapsed}");
            }
        }
    }
}

Output looks like this

Size: 10
Input: )))(()()()JerryNixon
Output: ()()()
Time: 00:00:00.0006158

Size: 10
Input: ()))))((((JerryNixon
Output: ()
Time: 00:00:00.0000317

Size: 10
Input: (())))))))JerryNixon
Output: (())
Time: 00:00:00.0000146

Size: 20
Input: )())()()((((((()))))JerryNixon
Output: ()()()((((()))))
Time: 00:00:00.0000115

Size: 30
Input: ))))((()))())(()()(()((()((())JerryNixon
Output: ((()))()()()()()(())
Time: 00:00:00.0000207

Some references:

A balancing group definition deletes the definition of a previously defined group and stores, in the current group, the interval between the previously defined group and the current group. This grouping construct has the following format:

(?<name1-name2>subexpression) or (?'name1-name2' subexpression)

Backreferences provide a convenient way to identify a repeated character or substring within a string. For example, if the input string contains multiple occurrences of an arbitrary substring, you can match the first occurrence with a capturing group, and then use a backreference to match subsequent occurrences of the substring.

@"(?<char>\w)\k<char>"

Alternation constructs modify a regular expression to enable either/or or conditional matching. .NET supports three alternation constructs:

1. Pattern matching with |
2. Conditional matching with (?(expression)yes|no)
3. Conditional matching based on a valid captured group