Magical String
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Description
A magical string s consists of only '1' and '2' and obeys the following rule:
- Concatenating the sequence of lengths of its consecutive groups of identical characters '1' and '2' generates the string s itself.
The first few elements of s is s = "1221121221221121122……". If we group the consecutive 1's and 2's in s, it will be "1 22 11 2 1 22 1 22 11 2 11 22 ......" and counting the occurrences of 1's or 2's in each group yields the sequence "1 2 2 1 1 2 1 2 2 1 2 2 ......".
You can see that concatenating the occurrence sequence gives us s itself.
Given an integer n, return the number of 1's in the first n number in the magical string s.
Example 1:
Example 2:
Solution