Subsequences with a Unique Middle Mode I

Description

Given an integer array nums, find the number of subsequences of size 5 of nums with a unique middle mode.

Since the answer may be very large, return it modulo 109 + 7.

A mode of a sequence of numbers is defined as the element that appears the maximum number of times in the sequence.

A sequence of numbers contains a unique mode if it has only one mode.

A sequence of numbers seq of size 5 contains a unique middle mode if the middle element (seq[2]) is a unique mode.