vault backup: 2022-09-06 17:14:03

OJ notes/pages/Leetcode Group-Anagrams.md

@@ -4,7 +4,7 @@
 
 > ##### Data structures:
 >
-> #DS #array #hash_table 
+> #DS #array #hash_table #two_way_hash_table
 >
 > ##### Difficulty:
 >
@@ -34,18 +34,24 @@ An **Anagram** is a word or phrase formed by rearranging the letters of a differ
 
 **Example 1:**
 
+```
 **Input:** strs = ["eat","tea","tan","ate","nat","bat"]
 **Output:** [["bat"],["nat","tan"],["ate","eat","tea"]]
+```
 
 **Example 2:**
 
+```
 **Input:** strs = [""]
 **Output:** [[""]]
+```
 
 **Example 3:**
 
+```
 **Input:** strs = ["a"]
 **Output:** [["a"]]
+```
 
 #### Constraints
 
@@ -58,7 +64,10 @@ An **Anagram** is a word or phrase formed by rearranging the letters of a differ
 > [!summary]
 > This is a #hash_table problem.
 
-This one can be solved simply using two-way hash tables, consisting two hash tables:
+#### Two way hash table
+
+This one can be solved simply using two-way hash tables, 
+consisting of two hash tables:
 - ana2id: turn anagram into an id
 - id2str: turn id into strings that has the anagrams
 
@@ -74,8 +83,21 @@ CPP-style initialization of C's array.
 Note that vectors doesn't work in unordered hash maps,
 unless we use custom hash functions.
 
+And arrays in c style definition (`int arr[26];`) will be 
+hashed according to address, not content.
+
+#### Alternative method
+
+By using sorted strings as keys, we can also solve this 
+problem.
+
+Since the input is lowercase English letters, counting
+sort can be used.
+
 ### Solution
 
+Two way hash table
+
 ```cpp
 class Solution {
 public:
@@ -109,4 +131,8 @@ public:
     return id2str;
   }
 };
-```
+```
+
+Counting sort
+
+#TODO: solve using counting sort