Given a string s, return the number of unique palindromes of length three that are a subsequence of s. Note that even if there are multiple ways to obtain the same subsequence, it is still only counted once. A palindrome is a string that reads the same forwards…

给定一个二进制数组 nums ( 索引从0开始 )。 我们将xi 定义为其二进制表示形式为子数组 nums[0..i] (从最高有效位到最低有效位)。

You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit).