I have a string read from another source such as "\\b\\bfoo\\bx". In this case, it would translate to the word "fox" as the first 2 \\b's are ignored, and the last 'o' is erased, and then replaced with 'x'. Also another case would be "patt\\b\\b\\b\\b\\b\\b\\b\\b\\b\\bfoo" should be translated to "foo"
I have come up with something using String.Replace, but it is complex and I am worried it is not working correctly, also it is creating a lot of new string objects which I would like to avoid.
Any ideas?
Probably the easiest is to just iterate over the entire string. Given your inputs, the following code does the trick in 1-pass
public string ReplaceBackspace(string hasBackspace)
{
if( string.IsNullOrEmpty(hasBackspace) )
return hasBackspace;
StringBuilder result = new StringBuilder(hasBackspace.Length);
foreach (char c in hasBackspace)
{
if (c == '\b')
{
if (result.Length > 0)
result.Length--;
}
else
{
result.Append(c);
}
}
return result.ToString();
}
The way I would do it is low-tech, but easy to understand.
Create a stack of characters. Then iterate through the string from beginning to end. If the character is a normal character (non-slash), push it onto the stack. If it is a slash, and the next character is a 'b', pop the top of the stack. If the stack is empty, ignore it.
At the end, pop each character in turn, add it to a StringBuilder, and reverse the result.
Regular expressions version:
var data = @"patt\b\b\b\b\b\b\b\b\b\bfoo";
var regex = new Regex(@"(^|[^\\b])\\b");
while (regex.IsMatch(data))
{
data = regex.Replace(data, "");
}
Optimized version (and this one works with backspace '\\b' and not with string "\\b"):
var data = "patt\b\b\b\b\b\b\b\b\b\bfoo";
var regex = new Regex(@"[^\x08]\x08", RegexOptions.Compiled);
while (data.Contains('\b'))
{
data = regex.Replace(data.TrimStart('\b'), "");
}
public static string ProcessBackspaces(string source)
{
char[] buffer = new char[source.Length];
int idx = 0;
foreach (char c in source)
{
if (c != '\b')
{
buffer[idx] = c;
idx++;
}
else if (idx > 0)
{
idx--;
}
}
return new string(buffer, 0, idx);
}
EDIT
I've done a quick, rough benchmark of the code posted in answers so far (processing the two example strings from the question, one million times each):
ANSWER | TIME (ms)
------------------------|-----------
Luke (this one) | 318
Alexander Taran | 567
Robert Paulson | 683
Markus Nigbur | 2100
Kamarey (new version) | 7075
Kamarey (old version) | 30902
You could iterate through the string backward, making a character array as you go. Every time you hit a backspace, increment a counter, and every time you hit a normal character, skip it if your counter is non-zero and decrement the counter.
I'm not sure what the best C# data structure is to manage this and then be able to get the string in the right order afterward quickly. StringBuilder
has an Insert
method but I don't know if it will be performant to keep inserting characters at the start or not. You could put the characters in a stack and hit ToArray()
at the end -- that might or might not be faster.
String myString = "patt\b\b\b\b\b\b\b\b\b\bfoo";
List<char> chars = myString.ToCharArray().ToList();
int delCount = 0;
for (int i = chars.Count -1; i >= 0; i--)
{
if (chars[i] == '\b')
{
delCount++;
chars.RemoveAt(i);
} else {
if (delCount > 0 && chars[i] != null) {
chars.RemoveAt(i);
delCount--;
}
}
}
i'd go like this: code is not tested
char[] result = new char[input.Length()];
int r =0;
for (i=0; i<input.Length(); i++){
if (input[i] == '\b' && r>0) r--;
else result[r]=input[i];
}
string resultsring = result.take(r);
创建一个StringBuilder并复制除退格字符之外的所有内容。
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