Split the string s into as many parts as possible so that each letter appears in at most one part. Return a list of the part sizes. Joined back together, the parts must give s.
s = "ababcbacadefegdehijhklij"[9,7,8] ("ababcbaca", "defegde", "hijhklij")s = "eccbbbbdec"[10]i: end = max(end, last[s[i]]), so the part stretchesi == end: cut ✂️, record end − start + 1, start a new partEvery letter forces an interval from its first to its last appearance, and a part can't cut through any interval. This is Merge Intervals in disguise: end is the right edge of the merged interval so far. Cutting the moment i == end is the earliest legal cut, and cutting early never hurts the rest of the string, so you get the maximum number of parts.
All distinct letters ("abc") → every letter is its own part: [1,1,1]. First letter also last ("abca") → one part covering everything. Remember to return sizes, not the strings. And start = i + 1 after each cut.