763. Partition Labels**

763. Partition Labels**

https://leetcode.com/problems/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.

Note:

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

C++ 实现 1

使用双指针. 首先明确一点, 要按题意对字符串进行分割, 必然要先对数组进行一次遍历, 只有这样, 拿题目中的例子来说, 我们才能知道 a 最远的位置在哪, 然后在第一个 a 和最后一个 a 之间, 判断中间的字符最远的位置是否有大于最后一个 a 的, 如果有的话, 就要更新最远的位置. 下面代码中, 我用 limit 来表示一个划分中最远的位置. 用 i 来记录一个划分中的起始位置, 用 j 来表示末尾位置.

class Solution {
public:
    vector<int> partitionLabels(string S) {
        unordered_map<char, int> record;
        vector<int> res;
        for (int i = 0; i < S.size(); ++ i) record[S[i]] = i;
        int i = 0;
        while (i < S.size()) {
            int j = i;
            int limit = record[S[i]];
            while (j < limit) {
                limit = std::max(record[S[j]], limit);
                ++ j;
            }
            res.push_back(j + 1 - i);
            i = ++ j;
        }
        return res;
    }
};