820. Short Encoding of Words

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

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.

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)Trie (Cây tiền tố)Prefix Sum (Tổng tiền tố)
⏱️ Thời gian O(n²)
💾 Không gian O(n)

💻 Lời Giải

Python 0820-short-encoding-of-words.py 
class Node:
    def __init__(self):
        self.children = defaultdict(Node)
        
class Trie:
    def __init__(self):
        self.root = Node()
        
    def insert(self, word: str) -> None:
        root = self.root
        for char in word:
            root = root.children[char]
    
    def isNotPrefix(self, word: str) -> bool:
        root = self.root
        for char in word:
            root = root.children[char]
        return len(root.children) == 0

class Solution:
    def minimumLengthEncoding(self, words: List[str]) -> int:
        answ = 0
        trie = Trie()
        
        words = list(set(words))
        
        for word in words:
            trie.insert(word[::-1])
            
        for word in words:
            answ += len(word) + 1 if trie.isNotPrefix(word[::-1]) else 0
            
        return answ