using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace SO13389560Balancing
{
class Program
{
static void Main(string[] args)
{
string s = "abcdefgh";
string pattern = @"(?<=(?<A>.)(?<-A>.))";
s = Regex.Replace(s, pattern, "!");
Console.WriteLine(s);
//Console.ReadKey();
}
}
}
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