LeetCode 763. Partition Labels

原题链接在这里：https://leetcode.com/problems/partition-labels/description/

题目：

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.

题解：

对于一个char, 找出她最先和最后出现的index. 然后像Merge Intervals结合交叉的部分.

可以先找出最后出现的index. 再iterate一遍, 每次遇到更大的最后出现index 便更新最远能跳的距离. 当到达最远能跳的距离时就说明到了融合后interval的末尾. 计算长度加到res中.

Time Complexity: O(S.length()). Space: O(1).

AC Java:

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;
        }
        
        List<Integer> res = new ArrayList<Integer>();
        int maxJump = 0;
        int start = 0;
        for(int i = 0; i<S.length(); i++){
            maxJump = Math.max(maxJump, last[S.charAt(i)-'a']);
            if(i == maxJump){
                res.add(i-start+1);
                start = i+1;
            }
        }
        
        return res;
    }
}