Partition a string into as many parts as possible so that each letter appears in at most one part.
With s = "ababcbacadefegdehijhklij":
- "ababcbaca" contains all 'a', 'b', 'c'. Length 9.
- "defegde" contains all 'd', 'e'. Length 7.
- "hijhklij" contains all 'h', 'i', 'j', 'k', 'l'. Length 8.
- Result: [9, 7, 8].
With s = "eccbbbbdec":
- "eccbbbbdec" must be one part (letters overlap throughout).
- Result: [10].
Return the list of partition sizes.
Constraints: s.length . All lowercase letters.