Add new file

def/count

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+##################################### Первый способ:
+
+A = [10, 10, 23, 10, 123, 66, 78, 123]
+counter = {}
+
+for elem in A:
+    counter[elem] = counter.get(elem, 0) + 1
+
+doubles = {element: count for element, count in counter.items() if count > 1}
+
+print(doubles)
+
+##################################### Второй способ:
+
+from collections import Counter
+counter = Counter(A)
+
+##################################### Третий способ:
+
+from collections import defaultdict
+counter = defaultdict(int)
+for elem in A:
+    counter[elem] += 1