2707. Extra Characters in a String

Problem Link

Description

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You are given a 0-indexed string s and a dictionary of words dictionary. You have to break s into one or more non-overlapping substrings such that each substring is present in dictionary. There may be some extra characters in s which are not present in any of the substrings.

Return the minimum number of extra characters left over if you break up s optimally.

 

Example 1:

Input: s = "leetscode", dictionary = ["leet","code","leetcode"]
Output: 1
Explanation: We can break s in two substrings: "leet" from index 0 to 3 and "code" from index 5 to 8. There is only 1 unused character (at index 4), so we return 1.

Example 2:

Input: s = "sayhelloworld", dictionary = ["hello","world"]
Output: 3
Explanation: We can break s in two substrings: "hello" from index 3 to 7 and "world" from index 8 to 12. The characters at indices 0, 1, 2 are not used in any substring and thus are considered as extra characters. Hence, we return 3.

 

Constraints:

• 1 <= s.length <= 50
• 1 <= dictionary.length <= 50
• 1 <= dictionary[i].length <= 50
• dictionary[i] and s consists of only lowercase English letters
• dictionary contains distinct words

Solution

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Python3

class Solution:
    def minExtraChar(self, s: str, dictionary: List[str]) -> int:
        N = len(s)
        d = set(dictionary)
 
        @cache
        def go(index):
            if index == N: return 0
 
            res = 1 + go(index + 1)
 
            for j in range(index, N):
                if s[index : j + 1] in d:
                    res = min(res, go(j + 1))
            
            return res
        
        return go(0)