Repeatedly eliminate a substring

I'm trying to pass a programming challenge where we are to replace all instances of a substring in a string until there are none left. So an input like

Pibabakekezza
 bake

Has output

Pizza

And if there is nothing left say so. I fail an unknown test case because I take longer than 1 second.

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Runtime;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Runtime.CompilerServices;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            GCLatencyMode oldMode = GCSettings.LatencyMode;

            // Make sure we can always go to the catch block, 
            // so we can set the latency mode back to `oldMode`
            RuntimeHelpers.PrepareConstrainedRegions();

            try
            {
                GCSettings.LatencyMode = GCLatencyMode.LowLatency;
                //Your code goes here
                string s =Console.ReadLine();
                string b =Console.ReadLine();
                while(s.Contains(b))
                {
                    s=s.Replace(b, "");
                }
                if(s!="")
                {
                    Console.WriteLine(s);
                }
                else
                {
                    Console.WriteLine("FRULA");
                }
            }
            finally
            {
                // ALWAYS set the latency mode back
                GCSettings.LatencyMode = oldMode;
            }
        }
    }
}

Restrictions:

1≤|bigString|≤1 000 000

1≤|substring|≤36

bigString and the substring string consist of uppercase and lowercase letters of the English alphabet and digits 0, 1, …, 9. The characters in the substring are all different.

CPU Time limit: 1 second
Memory limit: 10

As stated by 200_success +1 string is immutable

StringBuilder also has Replace but getting it to loop is trickier

You would need to time this

string s = "Pibabakekezza";
string r = "bake";
StringBuilder sb = new StringBuilder(s);
while (sb.Length != sb.Replace(r, "").Length) { }
Debug.WriteLine(sb.ToString());

A character can only be:

• start of replace

• in replace

• other

Not real clean code - this is more just the algorithm

I know should use { } on every if else

Store partial matches in a Stack

I tested with a very large hard input and it was 40 milliseconds

public static void QuickReplaceTest()
{
    string s = "Pibabakekezza";
    string r = "bake";
    Debug.WriteLine(QuickReplace2(s, r));
    Debug.WriteLine(QuickReplace3(s, r));

    s = "babakekePbakeibabbakeakebakekezbakezabake";
    r = "b";
    Debug.WriteLine(QuickReplace2(s, r));
    Debug.WriteLine(QuickReplace3(s, r));

    StringBuilder sb = new StringBuilder();
    sb.Append("piz");
    for (int i = 0; i  s.Length)
        return string.Empty;
    if (r.Length == 1)
        return(s.Replace(r, ""));

    StringBuilder sb = new StringBuilder(s.Length / 2);
    char[] rArray = r.ToCharArray();
    int rArrayLen = rArray.Length;
    Stack partialMatches = new Stack();   
    byte curMatchCount = 0;
    Stopwatch sw = new Stopwatch();
    sw.Start();
    foreach(char c in s)
    {
        //Debug.WriteLine(c);
        if (c == rArray[0])
        {
            if (curMatchCount > 0)
                partialMatches.Push(curMatchCount);
            curMatchCount = 1;
        }
        else if (c == rArray[curMatchCount])
        {
            curMatchCount++;
            if (curMatchCount == rArrayLen)
            {
                if (partialMatches.Count == 0)
                    curMatchCount = 0;
                else
                    curMatchCount = partialMatches.Pop();
            }
        }
        else
        {
            //need to unload the stack
            if (partialMatches.Count > 0)
            {
                foreach (int count in partialMatches.Reverse())
                    for (int i = 0; i  0)
    {
        foreach (int count in partialMatches.Reverse())
            for (int i = 0; i  s.Length)
        return string.Empty;
    if (r.Length == 1)
        return (s.Replace(r, ""));

    StringBuilder sb = new StringBuilder(s.Length / 2);
    char[] rArray = r.ToCharArray();
    int rArrayLen = rArray.Length;
    Stack partialMatches = new Stack();
    byte curMatchCount = 0;
    Stopwatch sw = new Stopwatch();
    sw.Start();
    foreach (char c in s)
    {
        sb.Append(c);
        if (c == rArray[0])
        {
            if (curMatchCount > 0)
                partialMatches.Push(curMatchCount);
            curMatchCount = 1;
        }
        else if (c == rArray[curMatchCount])
        {
            curMatchCount++;
            if (curMatchCount == rArrayLen)
            {
                sb.Length -= rArrayLen;
                if (partialMatches.Count == 0)
                    curMatchCount = 0;
                else
                    curMatchCount = partialMatches.Pop();
            }
        }
        else
        {
            curMatchCount = 0;
            partialMatches.Clear();
        }
    }
    sw.Stop();
    Debug.WriteLine(sw.ElapsedMilliseconds.ToString());
    return sb.ToString();
}

StackExchange Code Review Q#154836, answer score: 9