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763. Partition Labels

Medium

You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part.

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. 

Example 2:

Input: s = “eccbbbbdec”

Output: [10]

Constraints:

• 1 <= s.length <= 500
• s consists of lowercase English letters.

Solution

using System.Collections.Generic;

public class Solution {
    public IList<int> PartitionLabels(string s) {
        char[] letters = s.ToCharArray();
        IList<int> result = new List<int>();
        int[] position = new int[26];
        for (int index = 0; index < letters.Length; index++) {
            position[letters[index] - 'a'] = index;
        }
        int i = 0;
        int prev = -1;
        int max = 0;
        while (i < letters.Length) {
            if (position[letters[i] - 'a'] > max) {
                max = position[letters[i] - 'a'];
            }
            if (i == max) {
                result.Add(i - prev);
                prev = i;
            }
            i++;
        }
        return result;
    }
}

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