union

Subject

Assignment name  : union
Expected files   : union.c
Allowed functions: write
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Write a program that takes two strings and displays, without doubles, the
characters that appear in either one of the strings.

The display will be in the order characters appear in the command line, and
will be followed by a \n.

If the number of arguments is not 2, the program displays \n.

Example:

$>./union zpadinton "paqefwtdjetyiytjneytjoeyjnejeyj" | cat -e
zpadintoqefwjy$
$>./union ddf6vewg64f gtwthgdwthdwfteewhrtag6h4ffdhsd | cat -e
df6vewg4thras$
$>./union "rien" "cette phrase ne cache rien" | cat -e
rienct phas$
$>./union | cat -e
$
$>
$>./union "rien" | cat -e
$
$>

Commented solution

union.c

union.c

#include <unistd.h>

int main(int ac, char **av)
{
    // create a lookup table for all chars in ascii table
    int i = 0, lookup[256 = {0};
    
    if (ac == 3)
    {
        // loop over the whole first string
        // for each character, switch the value in
        // the lookup table
        while(av[1][i])
        	lookup[(int)av[1][i++]] = 1;
        i = 0;
        // do the same thing for the second string
        while(av[2][i])
        	lookup[(int)av[2][i++]] = 1;
        i = 0;
        
        // loop over the first string to write the
        // seen chars to the screen, switch back the
        // value in the lookup table once printed
        while (av[1][i])
        {
            if (lookup[(int)av[1][i]])
            {
                write(1, &av[1][i], 1);
                lookup[(int)av[1][i]] = 0;
            }
            i++;
        }
        i = 0;
        while (av[2][i])
        {
            if (lookup[(int)av[2][i]])
            {
                write(1, &av[2][i], 1);
                lookup[(int)av[2][i]] = 0;
            }
            i++;
        }
    }
    write(1, "\n", 1);
    return (0);
}