Partition Labels 分割字符串

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:

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

题意：将一个只有小写的字符串分段，每段中的字母只在本段出现，最多分几段。
解法：首先将每个字母在字符串中出现的最后位置记录下来，再次遍历字符串时，更新当前各字符的最远位置，直到当前位置等于最远位置就可以分割。

class Solution {
public:
    vector partitionLabels(string S) {
        vector a(26, 0);
        vector ans;
        for(int i = 0; i < S.size(); ++i)
            a[S[i] - 'a'] = i;
        
        int maxID = -1, lastID = 0;
        for(int i = 0; i < S.size(); ++i){
            maxID = max(maxID, a[S[i] - 'a']);
            if(i == maxID){
                ans.push_back(maxID - lastID + 1);
                lastID = i + 1;
            }
        }
        return ans;
    }
};