Powerset count

src/powerset.rs

@@ -3,7 +3,7 @@ use std::iter::FusedIterator;
 use std::usize;
 use alloc::vec::Vec;
 
-use super::combinations::{Combinations, combinations};
+use super::combinations::{Combinations, checked_binomial, combinations};
 use super::size_hint;
 
 /// An iterator to iterate through the powerset of the elements from an iterator.
@@ -81,6 +81,12 @@ impl<I> Iterator for Powerset<I>
             (0, self_total.1)
         }
     }
+
+    fn count(self) -> usize {
+        let k = self.combs.k();
+        let (n, combs_count) = self.combs.n_and_count();
+        combs_count + (k + 1..=n).map(|i| checked_binomial(n, i).unwrap()).sum::<usize>()
+    }
 }
 
 impl<I> FusedIterator for Powerset<I>