You are given a binary string s.
A prefix of s is considered valid if its characters can be rearranged to form an alternating string.
Return the number of valid prefixes of s.
A binary string is a string consisting only of '0' and '1'.
A prefix of a string is a substring that starts from the beginning of the string and extends to any point within it.
A substring is a contiguous non-empty sequence of characters within a string.
A string is considered alternating if no two adjacent characters are equal.
Example 1:
Input: s = "00101"
Output: 3
Explanation:
The valid prefixes are:
"0": It is already an alternating string."001": It can be rearranged into "010", which is an alternating string."00101": It can be rearranged into "01010", which is an alternating string.Thus, the answer is 3.
Example 2:
Input: s = "101"
Output: 3
Explanation:
All prefixes of s = "101" are already alternating strings. Thus, the answer is 3.
Constraints:
1 <= s.length <= 100s consists only of '0' and '1'.A binary string can be rearranged into an alternating string if the numbers of '0' and '1' differ by at most one.
Scan s from left to right, maintain the counts of both characters in the current prefix, and count the prefixes satisfying this condition.
"00101"
"101"