Leetcode763 Partition Labels

题目描述

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.

思路

将每一个字符与其对应的位置放入HashMap中，两个指针，start和end，end取end本身和所处理字符的位置中较大的那个值。如果i==end，则说明该字符串截取完毕，end-start+1为当前字符串得分长度并放入ans（list）中，直到最后一个字符循环结束。

代码

class Solution {
    public List<Integer> partitionLabels(String S) {
        HashMap<Character, Integer> map =  new HashMap<>();
        for(int i=0;i<S.length();i++){
            map.put(S.charAt(i),i);
        }
        List<Integer> ans =  new ArrayList<>();
        int start = 0;
        int end = 0;
        for(int i=0;i<S.length();i++){
            end = Math.max(end,map.get(S.charAt(i)));
            if(i == end){
                ans.add(end - start + 1);
                start = end +1;
            }
        }
        return ans;
    }
}

Note:

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