[leetcode]763. Partition Labels 分割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

题意

给你一个串， 要求分割尽量多份，使得每份中的字母只在该被分割部分出现

思路

扫一遍串，用一个map存每个字母的最大index值

扫一遍串，lock住start指针，更新即将被分割子串最大的last值，当last == i， 则找到一个被分割子串。 

代码

class Solution {
    public List<Integer> partitionLabels(String S) {
        if(S == null || S.length() == 0){return null; }
        List<Integer> list = new ArrayList<>();
        int[] map = new int[26];  

        for(int i = 0; i < S.length(); i++){
            map[S.charAt(i)-'a'] = i;
        }
        
        int last = 0;
        int start = 0;
        for(int i = 0; i < S.length(); i++){
            last = Math.max(last, map[S.charAt(i)-'a']);
            if(last == i){
                list.add(last - start + 1);
                start = last + 1;
            }
        }
        return list;
    }
}