You are given an integer array nums.

An integer x is special if all occurrences of x in nums appear in a single contiguous block.

Return the number of distinct special integers in nums.

Example 1:

Input: nums = [1,2,2,1]

Output: 1

Explanation:

1 appears at indices 0 and 3, forming two separate blocks, so it is not special.
2 appears in a single contiguous block at indices [1, 2], so it is special.

Therefore, there is one special integer.

Example 2:

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

Output: 2

Explanation:

3 appears in a single contiguous block at indices [0, 1], so it is special.
1 appears at indices 2 and 5, forming two separate blocks, so it is not special.
2 appears in a single contiguous block at indices [3, 4], so it is special.

Therefore, there are two special integers.

Constraints:

4038. Count Integers Appearing in a Single Block