763. Partition Labels

Question

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.

Solution

Method 1: Greedy

class Solution {
    public List<Integer> partitionLabels(String S) {
        int len = S.length();
        char[] arr = S.toCharArray();
        int cur = 0, last = 0, temp = 0, count = 0;
        Map<Character, Integer> map = findLast(arr);
        List<Integer> result = new ArrayList<>();
        while(cur < len){
            last = map.get(arr[cur]);
            temp = cur;
            while(temp < last){
                last = Math.max(last, map.get(arr[++temp]));
            }
            result.add(last - cur + 1);
            cur = last + 1;
        }
        return result;
    }
    private Map<Character, Integer> findLast(char[] arr){
        Map<Character, Integer> map = new HashMap<>();
        for(int i = arr.length - 1; i >= 0; i--){
            if(map.containsKey(arr[i])) continue;
            map.put(arr[i], i);
        }
        return map;
    }
}