Given an array of integers `nums`, return the number of good pairs.

A pair `(i, j)` is called good if `nums[i] == nums[j]` and `i` < `j`.

Example 1:

    Input: nums = [1,2,3,1,1,3]
    Output: 4
    Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.

Example 2:

    Input: nums = [1,1,1,1]
    Output: 6
    Explanation: Each pair in the array are good.

Example 3:

    Input: nums = [1,2,3]
    Output: 0

Constraints:

- `1 <= nums.length <= 100`
- `1 <= nums[i] <= 100`