Go4Expert - efficient way to check the duplicate characters from string2 in string1

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efficient way to check the duplicate characters from string2 in string1

Is there any other efficient manner of checking duplicate characters from string2 in string1

Code:

     char st1[6]="mikem";

      char st2[5]="Tame";

      int l1=strlen(st1);

      int l2=strlen(st2);

      int i,j;

      

     for( i=0;i<strlen(st2);i++)

     {

           

            for( j=0;j<l1;j++)

            {   if(st1[j]=='\0')

                continue;

                   

                if(st2[i]==st1[j])

                {    

                    st1[j]='\0';

                }

            }

       }

The above is checking each and every alphabet from st2 and replacing it with null in st1 ,if match is found

Is ther Any other more efficient way , rather than this one

-thank you

Re: efficient way to check the duplicate characters from string2 in string1

The algorithm you've presented operates in a time proportional to the lengths of the strings multiplied together, which might be O(n^2) (I don't know a lot about O() representation so that could be way off).
What you could do to improve matters is to run through the first string storing the number of times a particular character has occurred in a 26-number array (storing either the count or just whether or not a letter has been encountered, whichever is more relevant). Then just loop through the second string checking the array if that letter has been encountered.

Code:

        int i,flags[26];

        for (i=0; i<26; flags[i++]=0) ;

        char *str1="Hello";

        char *str2="World";

        for (i=0; str1[i]; i++)

                if (str1[i]>='a' && str1[i]<='z') flags[str1[i]-'a']=1;

        for (i=0; str2[i]; i++)

                if (str2[i]>='a' && str2[i]<='z' && flags[str2[i]-'a'])

                        putchar(str2[i]);

This should operate in O(n) time (if I'm correct about O() theory) because it operates in a time proportional to the lengths of the strings added together.
Output of the above is "ol".

Re: efficient way to check the duplicate characters from string2 in string1

Very nice! That would be hard to beat.
Using tolower() will deal with uppercase letters as well.

Code:

int i, n, flags[26];

char *str1="Hello";

char *str2="World";

for (i=0; i<26; flags[i++]=0)

  ;

for (i=0; str1[i]; i++) {

  n = tolower(str1[i]) - 'a';

  if (n >= 0 && n < 26)

    flags[n] = 1;

}

for (i=0; str2[i]; i++) {

  n = tolower(str2[i]) - 'a';

  if (n >= 0 && n < 26 && flags[n])

    putchar(str2[i]);

}

Re: efficient way to check the duplicate characters from string2 in string1

thank you everyone
yeah this definitely has less less complexity, than the previos..which I posted