Leetcode Algo Day6 | Hashtable Part1

Problem: 242. Valid Anagram

Time: 10min

Method: hashtable -  list

Reflection: To be a valid anagram, each letter can only be used once, so need a hashtable to count the letters. Set() does not work.

Time complexity: O(N)

Space complexity: O(1)

Problem: 349. Intersection of Two Arrays

Time: 2min

Method: hashtable - set

Reflection: set() returns unordered unique elements. Set is easy to implement, but more cost of space and time.

Time complexity: O(N+M)

Space complexity: O(N)

Problem: 202. Happy Number

Time: 

Method: hashtable -  list

Reflection: Hashtable is used to detect cycle. divmod() to get both divident and mode. After each loop, reset n = ssq.

Time complexity: O(logN)

Space complexity: O(logN)

Problem: 1. Two Sum

Time: 5min

Method: hashtable -  dict

Reflection: Quesiton prompt mentions exactly one solution. So can use hashtable to find the target pair by selecting from previously iterated elements in linear time.

Time complexity: O(N)

Space complexity: O(N)