Leetcode763-partitionLabels

Description

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

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.

3. Solution

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

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