763. Partition Labels(贪心)

Posted 2021-01-13 bernieloveslife

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.

class Solution:
    def partitionLabels(self, S):
        """
        :type S: str
        :rtype: List[int]
        """
        last = {} #记录每一个字母出现的最后的位置
        for  i in range(len(S)):
            last[S[i]] = i
        # print(last)
        start,end = -1,0 #start是下一个字段的首字母的前一个位置，第一个字段的首字母的位置一定是0
        res = []
        for i in range(len(S)):
            end = max(end,last[S[i]]) #不断更新末尾指针的位置
            if i==end: #当i指针的位置和末尾指针的位置相同时意味着[start,end]之间的字母的最后出现位置都在[start,end]，尾指针无法再更新
                res.append(end-start) #当前字段的长度
                start = end #start是下一个字段的首字母的前一个位置
        return res