763. Partition Labels

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.

解题要点：

先遍历一次，把每个字母最后出现的index记录下来。然后从第一位开始找它最后出现的位置，加到返回值里，并将起始值更新为这个位置的后一位，继续寻找。

class Solution {
    public List<Integer> partitionLabels(String S) {
        int[] lastIndex = new int[26];
        for(int i = 0; i < S.length(); i++){
            lastIndex[S.charAt(i) - 'a'] = i;
        }
        List<Integer> res = new ArrayList<>();
        int index1 = 0;
        while(index1 < S.length()){
            int index2 = index1;
            for(int i = index1; i < S.length() && i <= index2; i++){
                int index = lastIndex[S.charAt(i) - 'a'];
                index2 = Math.max(index, index2);
            }
            res.add(index2 - index1 + 1);
            index1 = index2 + 1;
        }
        return res;
    }
}