Programming Challenge!

[AceInfinity]

Here's a challenge for you guys !

Objective:
Write a function that returns the length of a string variable.

The Catch/Guidelines:
- Write a recursive function that only takes one parameter (of type string). Example:

public static int GetStrLen(string input)
{
	// Get the length of the string: input
	// Return the value for the length of this string
	// Keep in mind the rules...
{

- This cannot be an iterative function, it must be recursive
- You cannot use any counter variable to keep track
- You cannot use any of the properties available to the string class or type (depending on what language you're using). (Ex: No use of the Length property for strings in .NET, no len() in Python, etc...)

I completed this in C#, and Python so far, lets see who else can do it!

:thumbsup2:

 

[niemiro]

It is a good challenge, thank you.

Are we allowed to use any other variables at all?

I can figure out the majority of the approach, but I have yet to work out how to make it either work on every string (I can quite easily make it work by making it break for special case strings), or without an extra, non-counter variable (which is also easy). Now just to figure out a way without an extra variable and make it work with all strings. Hmmmmm.

 

[niemiro]

One C++ (untested pseudo-code) solution (using another variable):

Read More:

public static int GetStrLen(const char* input)
{
    static char* variable = NULL;

    if (variable == NULL)
        variable = &input;

    if (input[0] == '\0')
        return &input - variable;
    else
        return GetStrLen(input[1]);
}

It would be quite easy to convert this code to use a std::string (rather than const char*), but what I have written is slightly clearer, IMO.

I may have made a slight hash of it somewhere, maybe the length will be off by 1 or something, but I think (hope!) that the general idea is OK even if the code isn't.

 

[AceInfinity]

It is a good challenge, thank you.

Are we allowed to use any other variables at all?

I can figure out the majority of the approach, but I have yet to work out how to make it either work on every string (I can quite easily make it work by making it break for special case strings), or without an extra, non-counter variable (which is also easy). Now just to figure out a way without an extra variable and make it work with all strings. Hmmmmm.

You can use other variables if you want, but only local variables, no external member variables for counting.

One C++ (untested pseudo-code) solution (using another variable):

Read More:

public static int GetStrLen(const char* input)
{
    static char* variable = NULL;

    if (variable == NULL)
        variable = &input;

    if (input[0] == '\0')
        return &input - variable;
    else
        return GetStrLen(input[1]);
}

It would be quite easy to convert this code to use a std::string (rather than const char*), but what I have written is slightly clearer, IMO.

I may have made a slight hash of it somewhere, maybe the length will be off by 1 or something, but I think (hope!) that the general idea is OK even if the code isn't.

There's some issues in that code there, but you might be on the right track... :)

C# I did it this way:

Read More:

public static int GetStrLen(string input)
{
	return input == "" ? 0 : 1 + GetStrLen(input.Substring(1));
}

In Python I did it this way:

Read More:

def GetStrLen(strInput):
    if strInput == '':
        return 0
    return 1+GetStrLen(strInput[1:])

Which can also be done this way:

Read More:

def GetStrLen(strInput):
    if strInput == '':
        return 0
    return 1+GetStrLen(strInput[:-1])

 

[AceInfinity]

C++ solution that I came up with:

Read More:

[plain]int strLength(const char* input)
{
	string s = input;
	return s == "" ? 0 : 1 + strLength(s.substr(1).c_str());
}[/plain]

 

[niemiro]

Thank you for the clarification. Firstly, I realise I was being an idiot with my static variable I can easily do away with a whole if statement.

I will continue to think.

Richard

 

[tekz]

int func1(char cArray[])
{
    DWORD reg32_1, reg32_2;
    BYTE reg8_1;

    reg32_1 = (DWORD)cArray;
    reg32_2 = (DWORD)reg32_1 + 1;

    label1:
    reg8_1 = *(BYTE*)reg32_1;
    reg32_1++;

    if (reg8_1 != 0)
    {
        goto label1;
    }
    else
    {
        reg32_1 -= reg32_2;
        return reg32_1;
    }
}

lel

 

[AceInfinity]

int func1(char cArray[])
{
    DWORD reg32_1, reg32_2;
    BYTE reg8_1;

    reg32_1 = (DWORD)cArray;
    reg32_2 = (DWORD)reg32_1 + 1;

    label1:
    reg8_1 = *(BYTE*)reg32_1;
    reg32_1++;

    if (reg8_1 != 0)
    {
        goto label1;
    }
    else
    {
        reg32_1 -= reg32_2;
        return reg32_1;
    }
}

lel

It's not recursive however

 

[tekz]

Ahh sorry, my bad.
Nice solution, will battle with this some more later on, but this is probably most efficient way of doing it with recursive func.

 

[AceInfinity]

Might as well post a solution for c-strings:

size_t rstrlen(char *pstr)
{
  if (!*pstr) return 0;
  return rstrlen(pstr + 1) + 1;
}