[nimajneb]

So I've been doing software dev recruiting for a few months now and wanted to share something... after holding countless interviews and sitting in on MANY company/candidate interviews, one question seems to always come up in whiteboard sessions:

Show me how you would reverse a string.

With that said, thoughts on this question and how would YOU reverse a string in your prefered language?

[no2pencil]

nimajneb, on 09 March 2011 - 12:33 AM, said:

With that said, thoughts on this question and how would YOU reverse a string in your prefered language?

Determine the length of the string
Dump the strings value into an array
Set an integer variable to the length
Run through the values comparing the current value of the variable
Subtract for each instance of the loop
Repeat until the integer variable equals zero, outputing each element of the array to a 2nd array, or to standard output, depending on the request.

I have to admit, I've never been asked this during an interview. The question I always got asked most often is "Where do you see yourself within the company in five years?".

[nimajneb]

I think the point of the question is creativity and memory handling. I've seen some people completely blow it.

[Nikitin]

Is this like a first-round weed out question? What are some of the harder ones you ask?

P.S. By the way, this reminded me of one of the Google interviews. I had to answer about 4 algorithmic questions in 10 minutes. And one of the questions was something like this:

Say you have a singly linked list of N elements. You need to *append* to it the *reverse* of its first (N-1) elements.

So if you have A->B->C->D

Turn it into A->B->C->D->C->B->A

This post has been edited by Nikitin: 08 March 2011 - 11:51 PM

[tlhIn`toq]

These guys covered it pretty much to death.
http://stackoverflow...string-in-c-2-0

[codeprada]

I always get asked...Describe yourself for me. I had one programming job and i had to make a form and mail it in php.

This post has been edited by codeprada: 09 March 2011 - 06:23 AM

[raziel_]

tlhIn`toq, on 09 March 2011 - 03:14 PM, said:

These guys covered it pretty much to death.
http://stackoverflow...string-in-c-2-0

I personally would go with this:

public string Reverse(string text)
{
   if (text == null) return null;

   // this was posted by petebob as well 
   char[] array = text.ToCharArray();
   Array.Reverse(array);
   return array;
}

[dorknexus]

I would just walk through the string swapping characters at 0 and len -1, then 1 and len -2, and so on until the string was reversed. This allows you to reverse the string in place and not consume any additional memory besides a character for swaping.

something like:

void reverse(char *str, int len) {
    char tmp;
    int swap_index;

    for (int i = 0;i < (len /2);i++) {
        swap_index = len - (i + 1);
        tmp = str[swap_index];

        str[swap_index] = str[i];
        str[i] = tmp;
    }
}

This post has been edited by Dark_Nexus: 10 March 2011 - 01:18 AM

[baavgai]

Probably the most efficient, for the operations and storage, is to start at both ends:

void reverse(char *s, int len) {
	char *head = s, *tail = (s+len-1);
	while(head<tail) {
		char temp = *head;
		*head++ = *tail;
		*tail-- = temp;
	}
}

Or, for the non pointer crowd:

void reverse(char s[], int len) {
	for(int head = 0, tail=len-1; head<tail; head++, tail--) {
		char temp = s[head];
		s[head] = s[tail];
		s[tail] = temp;
	}
}

You should be able to write this in assembly with little trouble.

The goal is as few operations as possible; overall. Calling builtins can be very expensive, depending on what you're doing. Incrementing and decrementing are basic, so is compare. The more functions you pull in, the more overhead. Of course, the design philosophy of the language may be that I shouldn't have to worry about such things.

If you don't care about memory, then loading into another array would be acceptable. Indeed, it could be preferable.

This is more a question of language than approach. The above is valid for your run of the mill procedural language. Others might have more clever ways. A good functional language would use tail end recursion.

[Nov1ce]

Waz able to crack it using Java. I wanted to use C++ but I was having problems declaring strings and I did not want to use 'Char'. So if you got an idea on how to declare a string right-away I would appreciate (I use dev compiler). Anyways, this is the code::

import java.util.Scanner;
public class Reverse {
    public static void main(String[] args){
        Scanner read = new Scanner(System.in);

        String word;


        System.out.println("Enter the word you would like to reverse:");
        word = read.next();



        char wrd[] = word.toCharArray();
 
     int len = wrd.length;
    for(int i = len - 1; i >= 0; i--){
     System.out.print(wrd[i]);
    }


System.out.println();
    }
}

Don't forget to click the green button!!!

This post has been edited by macosxnerd101: 10 March 2011 - 05:54 AM
Reason for edit:: Please use code tags

[tlhIn`toq]

Even here you should use code tags

[Nov1ce]

Nov1ce, on 10 March 2011 - 05:18 AM, said:

Waz able to crack it using Java. I wanted to use C++ but I was having problems declaring strings and I did not want to use 'Char'. So if you got an idea on how to declare a string right-away I would appreciate (I use dev compiler). Anyways, this is the code::

import java.util.Scanner;
public class Reverse {
    public static void main(String[] args){
        Scanner read = new Scanner(System.in);

        String word;


        System.out.println("Enter the word you would like to reverse:");
        word = read.next();



        char wrd[] = word.toCharArray();
 
     int len = wrd.length;
    for(int i = len - 1; i >= 0; i--){
     System.out.print(wrd[i]);
    }


System.out.println();
    }
}

Don't forget to click the green button!!!

Hey you didn't have to vote me down I didn't know. Am kinda new!!!

[raziel_]

I think the point is to reverse a string the most efficient way. Not to just display it backward in console but nice try

[AdamSpeight2008]

1. Why do want to work us?

[AdamSpeight2008]

String Reversal in .net

Spoiler

 Dum revString= New String(theString.Reverse.ToArray)