GFG 94 Occurrences of 101

Geekina gifted Geek a number 'n', and since Geek is away, he asked you to count the number of

times the sequence "101" occurs as a subsequence in the binary representation of 'n'.

Example 1:

Input: 

n = 5

Output:

1

Explanation:

5 in binary is 101, hence "101" only occurring once as the subsequence.

Example 2:

Input: 

n = 21

Output:

4

Explanation:

21 in binary is 10101. "101" is occurring as a subsequence in 4 ways viz. - 

10101

10101

10101

10101

Your Task:  

You don't need to read input or print anything. Your task is to complete the

function count101() which takes an 64-bit integer n as the input and returns the count of number

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找101子序列的数量，当遇到1的时候，计算前面子字符串的10出现的次数，然后累加即可。

计算10出现的次数，单独写一个函数即可。