Backtracking to maximize the split of a string

 Here is the problem (medium difficulty, LC): https://leetcode.com/problems/split-a-string-into-the-max-number-of-unique-substrings/

1593. Split a String Into the Max Number of Unique Substrings

Medium

Given a string s, return the maximum number of unique substrings that the given string can be split into.

You can split string s into any list of non-empty substrings, where the concatenation of the substrings forms the original string. However, you must split the substrings such that all of them are unique.

A substring is a contiguous sequence of characters within a string.

 

Example 1:

Input: s = "ababccc"
Output: 5
Explanation: One way to split maximally is ['a', 'b', 'ab', 'c', 'cc']. Splitting like ['a', 'b', 'a', 'b', 'c', 'cc'] is not valid as you have 'a' and 'b' multiple times.

Example 2:

Input: s = "aba"
Output: 2
Explanation: One way to split maximally is ['a', 'ba'].

Example 3:

Input: s = "aa"
Output: 1
Explanation: It is impossible to split the string any further.

 

Constraints:

• 1 <= s.length <= 16

• s contains only lower case English letters.

Accepted

3,211

Submissions

9,144

Given the small boundaries we'll try a simple exponential approach with standard backtracking: keep splitting the string if you can (use a hashtable to keep track) and the moment that you've found a potential good split, check for the max one. Code is down below, cheers, ACC.

public class Solution {
    public int MaxUniqueSplit(string s)
    {
        int retVal = 0;
        MaxUniqueSplit(s, new Hashtable(), 0, ref retVal);
        return retVal;
    }

    private void MaxUniqueSplit(string s, Hashtable seen, int currentCount, ref int retVal)
    {
        if (String.IsNullOrEmpty(s))
        {
            retVal = Math.Max(retVal, currentCount);
            return;
        }

        string part = "";
        for (int i = 0; i < s.Length; i++)
        {
            part += s[i].ToString();
            if (!seen.ContainsKey(part))
            {
                seen.Add(part, true);
                MaxUniqueSplit(s.Substring(i + 1), seen, currentCount + 1, ref retVal);
                seen.Remove(part);
            }
        }
    }
}