If elements of array have  ≤ 10⁷ upper bound, so you can use array to count them. If they can be big numbers, I don't think there is better way than map (or unordered_map). Complexity will be O(1) while using array, O(logN) otherwise.

int cnt[10000000]; // declare this as global to prevent memory overflow.
for (int i = 1; i <= n; i++) {
    cin >> arr[i]; cnt[arr[i]]++;
}