How to remove repeating elements from an array in C - c

Question

I want to write a C program that removes repeated values in an array and keep only the last occurrence.
For example I have to arrays:
char vals[6]={'a','b','c','a','f','b'};
int pos[6]={1,2,3,4,5,6};
I want to write a function so that the elements in the array after would be:
char vals[4]={'c','a','f','b'};
int pos[4]={3,4,5,6};
I know how to delete elements in general but in this case I am looking for a way where I could also delete the values in the pos array (associated with the Vals array)

Answer 1

Overwriting duplicate elements, per se, isn't particularly complicated. But right here you have the additional constraint of wanting the last index of each element you find. This can be solved easily when you search for duplicates:
unsigned remove_duplicates (char * restrict array,
unsigned * restrict positions, unsigned count) {
// assume positions is uninitialized
unsigned current, insert = 0;
for (current = 0; current < count; current ++) {
// first, see if the value is already in the array
unsigned search;
for (search = 0; search < current; search ++)
if (array[current] == array[search]) break;
if (search < current)
// if we found it, we just have a new position for it
positions[search] = current + 1; // +1 because your positions are 1-based
else {
// otherwise, write it into the array and store its position
// insert tracks the insertion pointer (i.e., the new end of the array)
array[insert] = array[current];
positions[insert] = current + 1;
insert ++;
}
}
// at this point we're done; insert will have tracked the number of
// unique elements, which we can return as the new array size
// the positions won't be sorted; you can sort both arrays if you want
return insert;
}