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Posts published in “Hashtable”

花花酱 LeetCode 146. LRU Cache O(1)

Problem:

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.

get(key) – Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
put(key, value) – Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.

Follow up:
Could you do both operations in O(1) time complexity?

Example:

Idea:
Use Hashtable for fast mapping and double linked list for fast manipulation.
Time Complexity:
Put O(1)
Get O(1)
Solution:

 

花花酱 LeetCode 676. Implement Magic Dictionary

Problem:

Implement a magic directory with buildDict, and search methods.

For the method buildDict, you’ll be given a list of non-repetitive words to build a dictionary.

For the method search, you’ll be given a word, and judge whether if you modify exactly one character into another character in this word, the modified word is in the dictionary you just built.

Example 1:

Note:

  1. You may assume that all the inputs are consist of lowercase letters a-z.
  2. For contest purpose, the test data is rather small by now. You could think about highly efficient algorithm after the contest.
  3. Please remember to RESET your class variables declared in class MagicDictionary, as static/class variables are persisted across multiple test cases. Please see here for more details.
Idea:
Fuzzy match
Time Complexity:
buildDict: O(n*m)
n: numbers of words
m: length of word
search: O(m)
m: length of word
Space Complexity:
O(n*m)
Solution:

Java / Trie

Java / Trie v2