Absolute distinct count in a sorted array?

In this section we will see how to count how many of elements whose absolute values are distinct? Suppose in an array there are few elements like {5, 5, 6, -5, 8, 2, -2, 1}, so there are 8 elements. But there are 5 elements {5, 6, 8, 2, 1} which are distinct. The -5 and 5 are not considered as different, they are same as their absolute value is same.

To solve this problem, we will use the Set data-structure. In set duplicate elements are not allowed. And when we are inserting item into the set, we will push only the absolute value.

Algorithm

absoluteDistinctCount(arr)

begin
   define set s;
   for each element e in arr, do
      insert |e| into s
   done
   return the number of elements of s
end

Example

 Live Demo

#include<iostream>
#include<set>
#include<cmath>
using namespace std;
int absoluteDistinctCount(int arr[], int n){
   set<int> s;
   for(int i = 0; i<n; i++){
      s.insert(abs(arr[i])); //insert the absolute value
   }
   return s.size();
}
main() {
   int arr[] = {5, 5, 6, -5, 8, 2, -2, 1};
   int n = (sizeof(arr))/(sizeof(arr[0]));
   cout << "Absolute Distinct Count: " << absoluteDistinctCount(arr, n);
}

Output

Absolute Distinct Count: 5