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+# 2176. Count Equal and Divisible Pairs in an Array
+import collections
+from math import gcd
+
+"""
+given a 0-indexed integer array 'nums' of length 'n' and an integer 'k',
+return the number of pairs '(i, j)' where '0 <= i < j < n' such that 'nums[i]
+== nums[j]' and '(i * j)' is divisble by 'k'.
+"""
+
+
+class Solution(object):
+ def countPairs(self, nums, k):
+ """
+ :type nums: List[int]
+ :type k: int
+ :rtype: int
+ """
+ ids = collections.defaultdict(list)
+ for i, j in enumerate(nums):
+ ids[j].append(i)
+ ans = 0
+ for i in ids.values():
+ gcds = collections.Counter()
+ for j in i:
+ curr_i = gcd(j, k)
+ ans += sum(
+ cnt for curr_j, cnt in gcds.items() if curr_i * curr_j % k == 0
+ )
+ gcds[curr_i] += 1
+ return ans
+
+
+if __name__ == "__main__":
+ obj = Solution()
+ print(obj.countPairs(nums=[3, 1, 2, 2, 2, 1, 3], k=2))
+ print(obj.countPairs(nums=[1, 2, 3, 4], k=1))