Question
A chat quality tool flags key-smash by finding the character behind the longest streak. Given a non-empty message, return the character of the longest run of consecutive identical characters, as a one-character string. If several runs tie for longest, return the one that appears first. For example, 'heyyy nooo' returns 'y' (its run of 3 starts before the 'o' run of 3).
longest_run_char(message: str) → str["heyyy nooo"]out"y"State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.