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One of My Interview Questions Today

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  • J jon 80

    It's interesting that you swapped characters around; however VS2005 was crashing on me when I was walking through it with the debugger. Unhandled exception at 0x00412e00 in TestConsole4.exe: 0xC0000005: Access violation writing location 0x004156a4. It seems like the pointer is expected to be declared in a different manner with VS2005.

    Jon

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    R Offline
    realJSOP
    wrote on last edited by
    #30

    Usage:

    char\* sTemp = new char\[6\];
    strcpy(sTemp, "string");
    reverse(sTemp);
    delete\[\] sTemp;
    

    "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
    -----
    "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

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    • C cmk

      That's the way i've usually seen it done, i use something like:

      bool strrev_ip( char *s )
      {
      if( !s ) return(false);

      char *e = s + strlen(s)-1;

      for( ; s < e; s++, e-- ) {
      *s ^= *e;
      *e ^= *s;
      *s ^= *e;
      }

      return(true);
      }

      [EDIT] ... ummm, post order is screwed up, this was in reply to Nish ... and Dan didn't reply to this [/EDIT]

      ...cmk Save the whales - collect the whole set

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      nsoneja
      wrote on last edited by
      #31

      cmk wrote:

      That's the way i've usually seen it done, i use something like: bool strrev_ip( char *s ){ if( !s ) return(false); char *e = s + strlen(s)-1; for( ; s < e; s++, e-- ) { *s ^= *e; *e ^= *s; *s ^= *e; } return(true);}

      Nice touch adding the xor way of swapping variables...that's usually a separate interview question in its own right! Also, precludes using a temp variable, which could come across as a loophole (ie; instead of allocating another string)...Hmm can't imagine how they would do it vastly differently than whats outlined in the original posting, all seem to be some variation of swapping chars till the pointers cross over

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      • N Nish Nishant

        John Simmons / outlaw programmer wrote:

        but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me).

        I believe it's more common to have a char* to firstPos and a char* to lastPost, and then increment firstPos while decrementing lastPos. You basically did the same except that you avoided pointers and used the array index directly. Depending on his attitude he could take that in a good way (you know how to simplify algorithms and avoid unwanted pointer complexity) but he could also take it in a bad way (as in you were nervous about using pointers directly). Good luck anyhow. :)

        Regards, Nish


        Nish’s thoughts on MFC, C++/CLI and .NET (my blog)
        My latest book : C++/CLI in Action / Amazon.com link

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        Mike Dimmick
        wrote on last edited by
        #32

        The compiler will quite likely turn the array indexing into pointer arithmetic operations anyway. This is quite a simple optimization. I prefer to write array-indexing syntax as I find it less confusing.

        Stability. What an interesting concept. -- Chris Maunder

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        • R realJSOP

          Write a function that reverses the contents of a null-terminated string in place. The only limitation is that you can't allocate a new string during any part of the process. This is what I gave them:

          void ReverseString(char* str)
          {
          int len = strlen(str);
          int delta = len / 2;
          char pivot;
          for (int i = 0; i < delta; i++)
          {
          pivot = str[i];
          str[i] = str[len - i - 1];
          str[len - i - 1] = pivot;
          }
          }

          I know, it's not all that impressive, but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me). BTW, I feel that both of the interviews I did today went well. I fully expect to get offers on from each company.

          "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
          -----
          "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

          E Offline
          E Offline
          ednrgc
          wrote on last edited by
          #33

          My guess is that they were really looking for the recursive version.

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          0
          • R realJSOP

            Write a function that reverses the contents of a null-terminated string in place. The only limitation is that you can't allocate a new string during any part of the process. This is what I gave them:

            void ReverseString(char* str)
            {
            int len = strlen(str);
            int delta = len / 2;
            char pivot;
            for (int i = 0; i < delta; i++)
            {
            pivot = str[i];
            str[i] = str[len - i - 1];
            str[len - i - 1] = pivot;
            }
            }

            I know, it's not all that impressive, but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me). BTW, I feel that both of the interviews I did today went well. I fully expect to get offers on from each company.

            "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
            -----
            "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

            T Offline
            T Offline
            Tomz_KV
            wrote on last edited by
            #34

            It does not allow to allocate a string. I am wondering if it is ok to use a CharArray (string.ToCharArray()) and then use the reverse method to do it.

            Tom Z. (PMA)

            1 Reply Last reply
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            • E ednrgc

              My guess is that they were really looking for the recursive version.

              R Offline
              R Offline
              realJSOP
              wrote on last edited by
              #35

              On a long string, you will exhaust available stack space , not to mention the time overhead involved in repeatedly calling the function. Therefore, a recursive function is not an appropriate answer. -- modified at 11:08 Tuesday 24th July, 2007

              "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
              -----
              "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

              1 Reply Last reply
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              • D Dan Neely

                recursive, how WTFworthy. :rolleyes:

                -- You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer

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                J Offline
                jrbirdman
                wrote on last edited by
                #36

                Well, duh. Everyone knows that you don't type code anymore! It's keyboarded. Stupid VB programmers. :) Someone who likes it both ways, uh huh!

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                • R realJSOP

                  Actually, it's not so much a "can-you-do-it" question as much as it is a "how-would-you-approach-it" question.

                  "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                  -----
                  "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

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                  M Offline
                  Michael J Collins
                  wrote on last edited by
                  #37

                  I had to look up null terminated. I suck.. :( Seriously, I've been programming for 8 years (not including the 10,20 basic way back in the day), yet every time I see something like this I wonder what the hell I've really learned in all that time. It's discouraging.

                  Michael J. Collins Web Application Programmer

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                  0
                  • R realJSOP

                    Actually, it's not so much a "can-you-do-it" question as much as it is a "how-would-you-approach-it" question.

                    "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                    -----
                    "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

                    P Offline
                    P Offline
                    Paul Conrad
                    wrote on last edited by
                    #38

                    John Simmons / outlaw programmer wrote:

                    it is a "how-would-you-approach-it" question

                    That would make more sense.  To see what kind of thinker one is.

                    "The clue train passed his station without stopping." - John Simmons / outlaw programmer

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                    • M Michael J Collins

                      I had to look up null terminated. I suck.. :( Seriously, I've been programming for 8 years (not including the 10,20 basic way back in the day), yet every time I see something like this I wonder what the hell I've really learned in all that time. It's discouraging.

                      Michael J. Collins Web Application Programmer

                      J Offline
                      J Offline
                      jim_taylor
                      wrote on last edited by
                      #39

                      Michael, Back in ancient times (ca.1966) my friend Richard Pratt and I had a little contest, coding a binary search in IBM 360 assembler. At the end we were fighting to remove individual cycles from the loop. When we agreed he had won, reaching the irreducible minimum loop time, Dick Giering showed up with a faster method in hand. His algorithm wasted "lots" of time at the start building a halving table. Once he had the table built, his search ran almost twice as fast as our best effort, because he didn't have a divide instruction inside the loop. Don't feel bad. As the saying goes, "Ve get too soon oldt, und too late schmart." JimT

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                      • R realJSOP

                        Memory must have been an issue. Otherwise, the requirement would not have been stated the way it was. I could have knocked two more cycles off the cpu load, but it would have cost them 4 more bytes of memory.

                        "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                        -----
                        "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

                        R Offline
                        R Offline
                        rnot
                        wrote on last edited by
                        #40

                        An interesting variation I was faced with in an interview last year was this: Reverse the order of the words in a string in place. You get one character of memory and can assign pointers.

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                        • R realJSOP

                          Write a function that reverses the contents of a null-terminated string in place. The only limitation is that you can't allocate a new string during any part of the process. This is what I gave them:

                          void ReverseString(char* str)
                          {
                          int len = strlen(str);
                          int delta = len / 2;
                          char pivot;
                          for (int i = 0; i < delta; i++)
                          {
                          pivot = str[i];
                          str[i] = str[len - i - 1];
                          str[len - i - 1] = pivot;
                          }
                          }

                          I know, it's not all that impressive, but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me). BTW, I feel that both of the interviews I did today went well. I fully expect to get offers on from each company.

                          "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                          -----
                          "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

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                          C Offline
                          clydecraig
                          wrote on last edited by
                          #41

                          I don't have a c++ compiler on hand to prove it, but I think this code does the trick for single-byte character sets: void ReverseString(char* str) { char* end = strrchr(str, 0); while(str < --end) { str ^= end; end ^= str; str++ ^= end--; } }

                          C 1 Reply Last reply
                          0
                          • P Paul Conrad

                            John Simmons / outlaw programmer wrote:

                            Memory must have been an issue. Otherwise, the requirement would not have been stated the way it was.

                            Maybe they just wanted to have you think about a solution from a different perspective?  Not sure why they would have a seasoned programmer like yourself write code example to prove yourself.

                            "I've seen more information on a frickin' sticky note!" - Dave Kreskowiak

                            P Offline
                            P Offline
                            Peter Mulholland
                            wrote on last edited by
                            #42

                            Joel on Software suggested reversing a string as an interview question as an article some time ago. I got the same question in an interview almost 12 months ago and I think more developers are using it in interviews based on the Joel on Software article. He also gave some explanation of the conclusions you can draw from the solution given by the interviewee. http://www.joelonsoftware.com/articles/fog0000000073.html -- modified at 5:39 Wednesday 25th July, 2007

                            P 1 Reply Last reply
                            0
                            • R realJSOP

                              Write a function that reverses the contents of a null-terminated string in place. The only limitation is that you can't allocate a new string during any part of the process. This is what I gave them:

                              void ReverseString(char* str)
                              {
                              int len = strlen(str);
                              int delta = len / 2;
                              char pivot;
                              for (int i = 0; i < delta; i++)
                              {
                              pivot = str[i];
                              str[i] = str[len - i - 1];
                              str[len - i - 1] = pivot;
                              }
                              }

                              I know, it's not all that impressive, but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me). BTW, I feel that both of the interviews I did today went well. I fully expect to get offers on from each company.

                              "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                              -----
                              "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

                              P Offline
                              P Offline
                              prashant_jalasutrram
                              wrote on last edited by
                              #43

                              Hi, Very Good question and i having 3 1/2 years experience also could not get a clue.Really felt guilty. Thanks for sharing this Q&A. Thanks Prashant

                              prashant_vijaywada

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                              • C clydecraig

                                I don't have a c++ compiler on hand to prove it, but I think this code does the trick for single-byte character sets: void ReverseString(char* str) { char* end = strrchr(str, 0); while(str < --end) { str ^= end; end ^= str; str++ ^= end--; } }

                                C Offline
                                C Offline
                                clydecraig
                                wrote on last edited by
                                #44

                                (amended from previous post) I don't have a c++ compiler on hand to prove it, but I think this code does the trick for single-byte character sets: void ReverseString(char* str) { char* end = strrchr(str, 0); while(str < --end) { *str ^= *end; *end ^= *str; *str++ ^= *end--; } }

                                C 1 Reply Last reply
                                0
                                • C clydecraig

                                  (amended from previous post) I don't have a c++ compiler on hand to prove it, but I think this code does the trick for single-byte character sets: void ReverseString(char* str) { char* end = strrchr(str, 0); while(str < --end) { *str ^= *end; *end ^= *str; *str++ ^= *end--; } }

                                  C Offline
                                  C Offline
                                  clydecraig
                                  wrote on last edited by
                                  #45

                                  (amended from previous post -- again) I don't have a c++ compiler on hand to prove it, but I think this code does the trick for single-byte character sets: void ReverseString(char* str) { char* end = strrchr(str, 0); while(str < --end) { *str ^= *end; *end ^= *str; *str++ ^= *end; } }

                                  1 Reply Last reply
                                  0
                                  • R realJSOP

                                    Write a function that reverses the contents of a null-terminated string in place. The only limitation is that you can't allocate a new string during any part of the process. This is what I gave them:

                                    void ReverseString(char* str)
                                    {
                                    int len = strlen(str);
                                    int delta = len / 2;
                                    char pivot;
                                    for (int i = 0; i < delta; i++)
                                    {
                                    pivot = str[i];
                                    str[i] = str[len - i - 1];
                                    str[len - i - 1] = pivot;
                                    }
                                    }

                                    I know, it's not all that impressive, but the interviewer told me I'm the only person he's seen do it that way (which seemed odd to me). BTW, I feel that both of the interviews I did today went well. I fully expect to get offers on from each company.

                                    "Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
                                    -----
                                    "...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

                                    U Offline
                                    U Offline
                                    User of Users Group
                                    wrote on last edited by
                                    #46

                                    function = std::reverse( sz, sz + strlen(sz)); Regards, Not Joel or pointer arithmetic interviewer

                                    1 Reply Last reply
                                    0
                                    • P Peter Mulholland

                                      Joel on Software suggested reversing a string as an interview question as an article some time ago. I got the same question in an interview almost 12 months ago and I think more developers are using it in interviews based on the Joel on Software article. He also gave some explanation of the conclusions you can draw from the solution given by the interviewee. http://www.joelonsoftware.com/articles/fog0000000073.html -- modified at 5:39 Wednesday 25th July, 2007

                                      P Offline
                                      P Offline
                                      Paul Conrad
                                      wrote on last edited by
                                      #47

                                      Like John had said, it was more about how to think out the problem rather than can you do it or not.

                                      "The clue train passed his station without stopping." - John Simmons / outlaw programmer

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