Function problem

**Cyberman86** · 05-06-2009

I really don't know how to write the function part although i tried I'm not sure if it makes sense, I'm a beginner and sometimes i can't tell where i messed up.

Suppose we declare int a[N], b[M], c[N], where N and M are predefined
global constants, somewhat we initialize a and b such that they contain two sets and assume that the values in a and b are already sorted in ascending order (so you don’t need to anything
else, but use them as is).
NOW, We are interested in finding:
a. the difference between a and b, and put the elements of a-b into c and
b. the number of elements in c.

Write a function that will take a, b, c as parameters and determine the difference set c and the number of elements in c. The function will return the number of elements in c while storing the
difference between a and b into c.

For example, if a = {2, 5, 7, 8, 13} and b = {1, 5, 7, 9, 12}, then your function
will return 3 as the number of elements in c,
and we will have c = {2, 8, 13} as a-b.

Code:

int set_difference(int a[N], int b[M], int c[N])

{

int i;

for (i=0; i<b; i++) {

if ( x[N]==c)

return i;

else if (x[N] > c)




}
return (-1);
}

**root4** · 05-06-2009

try to explain your algorithm in english or any pseudo code, then we can discuss it to get proper c.

**Brafil** · 05-08-2009

He means subtracting two arrays (pseudo-sets) and store the result in c. You could use this (It's kinda slow, O(n²) performance)

Code:

int function(int a[N], int b[M], int c[N])
{
    for every element in a
        for every element in b
            if the element in a matches the element in b
                set a flag
        if the flag is not set
            add the element in a to c
    return the size of c
}

Of course, if the arrays are 100% sorted, you could use binary search. Maybe that would be faster.

**quzah** · 05-08-2009

Your example is wrong, or I'm too tired to interpret it correctly:

Write a function that will take a, b, c as parameters and determine the difference set c and the number of elements in c. The function will return the number of elements in c while storing the
difference between a and b into c.

For example, if a = [2, 5, 7, 8, 13] and b = [1, 5, 7, 9, 12], then your function
will return 3 as the number of elements in c,
and we will have c = [2, 8, 13] as a-b.

Shouldn't C be: [2, 8, 9, 12, 13]? It's basically finding all the elements between the two that don't match, right? Or is it supposed to just find the ones in A that aren't in B? If it's not the latter, then your example is wrong.

Quzah.

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