Longest Same-Character Run

Given a lowercase string, find the longest contiguous substring made of one repeated character. If several runs have the same maximum length, return the rightmost run encoded as `<character><length>`. Requirements Input: a lowercase English string source. Find the longest contiguous substring consisting of the same character. If multiple substrings tie for the same maximum length, choose the rightmost one. Return a string made of that character concatenated with the run length. Constraints: 1 <= source.length <= 100. Examples source = "bbacccdbbab" -> "c3" There are two a runs of length 1, three b runs with lengths 2, 2, and 1, and one c run of length 3. The longest run is ccc, so return c3. source = "bbaacaa" -> "a2" The maximum run length is 2 for bb, aa, and the final aa; choose the rightmost maximum, so return a2. Notes Scan once, tracking the current run character and length. When a run closes, update the best answer if current_len >= best_len; the >= is what implements the rightmost tie-break. Be careful to process the final run after the loop. A sentinel or a helper commit_run() avoids the common off-by-one. Preparation Write the one-pass version from scratch and test three cases: all one character, all unique characters, and a rightmost tie. Drill the tie-break deliberately: replacing >= with > silently returns the leftmost maximum and fails the second worked example.