820. Short Encoding of Words

Medium

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A valid encoding of an array of words is any reference string s and array of indices indices such that:

• words.length == indices.length

• The reference string s ends with the '#' character.

• For each index indices[i], the substring of s starting from indices[i] and up to (but not including) the next '#' character is equal to words[i].

Given an array of words, return the length of the shortest reference string s possible of any valid encoding of words.

Example 1:

Input: words = ["time", "me", "bell"]
Output: 10
Explanation: A valid encoding would be s = "time#bell#" and indices = [0, 2, 5].
words[0] = "time", the substring of s starting from indices[0] = 0 to the next '#' is underlined in "time#bell#"
words[1] = "me", the substring of s starting from indices[1] = 2 to the next '#' is underlined in "time#bell#"
words[2] = "bell", the substring of s starting from indices[2] = 5 to the next '#' is underlined in "time#bell#"

Example 2:

Input: words = ["t"]
Output: 2
Explanation: A valid encoding would be s = "t#" and indices = [0].

Constraints:

• 1 <= words.length <= 2000

• 1 <= words[i].length <= 7

• words[i] consists of only lowercase letters.

class Solution:
    def minimumLengthEncoding(self, words: List[str]) -> int:
        trie, ans = {}, 0
        for word in words:
            node = trie
            for c in word[::-1]:
                if '$' in node: 
                    ans -= node.pop('$')
                node = node.setdefault(c, {})
            if not node:
                node['$'] = len(word) + 1
                ans += node['$']
        return ans