763.Partition-Labels

763. Partition Labels

题目地址

https://leetcode.com/problems/partition-labels/

题目描述

A string S of lowercase English 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 English letters ('a' to 'z') only.

代码

Approach #1 Greedy

Time: O(N) && Space: O(1)

class Solution {
    public List<Integer> partitionLabels(String S) {
        int[] last = new int[26];
        for (int i = 0; i < S.length(); i++) {
            last[S.charAt(i) - 'a'] = i;
        }
        int j = 0, anchor = 0;
        List<Integer> ans = new ArrayList();
        for (int i = 0; i < S.length(); i++) {
            j = Math.max(j, last[S.charAt(i) - 'a']);
            if (i == j) {
                ans.add(i - anchor + 1);
                anchor = i + 1;
            }
        }

        return ans;
    }
}