how to detect duplicates in arrays & print non duplicates? - c

Question

void main ()
{
int x[19]={0}, i=0, y=0, u=0, p;
while (i<=19)
{
scanf("%d",&x[i]);
i=i+1;
}
for (i=u;i<=19;i++)
{
if (x[y]!=x[i+1])
p=x[y];
else
{
u++;
y++;
}
}
printf("%d",p);
}
So I used this to check for duplicates & it should print non duplicates, but as you can see this works if all are duplicates but one, as in
x[0]=1 x[1]=1 x[3]=9 x[4]=1 ... x[19]=1;
prints
9
So how to print non duplicates ? Any help ?

Answer 1

This would be the easiest solution, simply nest an additional for-loop. However, this takes O(n^2). Depending on the size of the array, it could be beneficial to look at a fast sort.
void main() {
int x[4] = { 1, 3, 2, 1 };
size_t i, j;
for (i = 0; i < sizeof(x) / sizeof(int); i ++) {
// Note that we only have to go to the last value before i.
for (j = 0; j < i; j ++) {
// We break if the value is a duplicate.
if (x[i] == x[j])
break;
}
// Check if the inner loop was break'ed (j < i) or not (j == i).
if (j == i)
printf("Unique: %i\n", x[i]);
}
}
One more thing: only use sizeof(x) / sizeof(int) if the size of x is known during compilation. This is the case here, but don't use it with malloc.

Answer 2

One of the simplest ways is to sort the array to group the duplicates together. Then, as you go through the array you only print a number if its different from the number that came before.
// Print the unique elements of a sorted array:
for(int i=0; i<N; i++){
if (i-1 >= 0 && arr[i] == arr[i-1]) { continue; }
if (i+1 < N && arr[i] == arr[i+1]) { continue; }
printf("%d\n", arr[i]);
}
To sort the array you can use the qsort function

Answer 3

void main ()
{
int num[20]={0}, i=0, n=0, index_num=0, init_incr=0, unique=0, n_uniq=1, temp, check=0;
while (i<=19)
{
printf("%02d- ",i+1);
scanf("%d",&num[i]);
i=i+1;
}
for (index_num=0;index_num<19;index_num++)
{
for (n=init_incr+index_num;n<19;n++)
{
if (num[index_num]!=num[index_num+1] && num[index_num]!=num[index_num-1])
{
check++;
temp=num[index_num];
unique=temp;
for (;n_uniq<=check;n_uniq++)
printf("\tunique %02d = %d\n", n_uniq, unique);
break;
}
}
}
}