469. Distinct Elements Difference

Given two integer arrays arr1 and arr2, return the number of distinct elements in arr1 that do not appear in arr2.

Example:
Input: arr1 = [1, 2, 3, 3], arr2 = [2, 4]
Output: 2
Explanation: The distinct elements in arr1 are 1, 2, and 3. Among these, 1 and 3 do not appear in arr2.

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