[LeetCode] 763. Partition Labels

Posted 2021-01-14 C·Moriarty

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：尽可能的把一个数组分解成多个，分解原则，相同的字母只能出现在一个数组里

贪心的典型例子，关键在于每个字母最后出现的位置，每次都更新最大(位置靠后的那个)，以那个为界拆就行了

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> list = new ArrayList<>();
        int i = 0;
        while (i < S.length()) {
            int j = lastIndex[S.charAt(i) - ‘a‘];
            for (int k = i; k < j; k++) {
                if (lastIndex[S.charAt(k) - ‘a‘] > j)
                    j = lastIndex[S.charAt(k) - ‘a‘];
            }
            list.add(j - i + 1);
            if (j == S.length() - 1)
                break;
            i = j + 1;
        }
        return list;
    }
}