Grouped Binary Substrings

Count substrings of a binary string where the number of `0`s equals the number of `1`s and all `0`s and all `1`s appear in two contiguous groups, such as `000111`, `111000`, `01`, or `10`. Requirements Input: a string containing only 0 and 1. Count substrings satisfying both conditions: equal number of 0s and 1s all identical characters are grouped into two contiguous runs Valid examples of shape: 000111, 111000, 01, 10. Return the count. Notes This is the same algorithmic family as LC 696 when the OA phrases it with grouped binary substrings. Compress the string into run lengths. For each adjacent pair of runs, add min(prev_run_len, cur_run_len). Do not enumerate substrings. The linear run-length solution is shorter and avoids timeouts. Preparation Implement the run-length scan in one pass while tracking prev and cur run lengths. Test alternating input (010101), one long block followed by a short block, and all-identical input.