Partition Labels - LeetCode

A string S of lowercase letters is given. We want to partition this string into as many parts as possible so that each letter appears in at most one part, and return a list of integers representing the size of these parts.

Example 1:

Input: S = "ababcbacadefegdehijhklij"
Output: [9,7,8]
Explanation:
The partition is "ababcbaca", "defegde", "hijhklij".
This is a partition so that each letter appears in at most one part.
A partition like "ababcbacadefegde", "hijhklij" is incorrect, because it splits S into less parts.

Note:

1. S will have length in range [1, 500].
2. S will consist of lowercase letters ('a' to 'z') only

Java Solution:

class Solution {
    public List<Integer> partitionLabels(String S) {
        List<Integer> partitionlengths = new ArrayList<>();
        int[] lastIndexes = new int[26];
        for(int i=0 ; i < S.length() ; i++){
            lastIndexes[S.charAt(i)-'a'] = i;
        }
        
        int i = 0;
        while(i < S.length()){
            int end = lastIndexes[S.charAt(i) - 'a'];
            int j = i;
            while(j !=end){
                end = Math.max(end,lastIndexes[S.charAt(j++)-'a']);
            }
            partitionlengths.add(j-i+1);
            i = j+1;
        }
        return partitionlengths;
    }
}