feat: change the implementation of count-even

Author: art049

tests/test_count_even.py

@@ -3,7 +3,11 @@
 
 def count_even(arr: list[int]) -> int:
     """Count the number of even numbers in an array."""
-    return sum(1 for x in arr if x % 2 == 0)
+    even = 0
+    for num in arr:
+        if num % 2 == 0:
+            even += 1
+    return even
 
 
 # Your tests can also be benchmarks