DFS notes

When to use dfs? Generally speaking, there are several situations as follows: Combination Sample answer: combination sum2  Key Point: 1) sorting before dfs 2) use Index to help remove duplicates 3) consider out of boundary question whenever using arrays Use DFS without recursion: Use STACK(Every time pop an item, push the it’s children, thus accomplish DFS) Stack FILO … More DFS notes

Graph

Initialize a graph in java Usually, we use Hashmap to store a graph in java. Because in hashmap/hashset, there won’t be a duplicate even if we repeat putting a same item in the map/set. Here is a template of initializing a hashmap graph:

Breadth First Search

Template: If a layer traversal is needed, add a “for” loop. (Attention that queue.size will change). If in a graph, we need a hash set to store the statue of node ( visited or not), and check set.contains(child) before offerring it into queue.  

Java Notes(1) String and Int

1.Initialization String a ; a must be initialized if further operations will be taken (unless assignment). eg. String a = null; a += “aaa”; System.out.println(a); This will print “nullaaa”. 2. Int to String to Int String a = Integer.toString(i); Int a = Integer.parseInt(a);  

Start MySQL server

I decided to write some technical blog on this site. But I’m not a native English speaker, I will try my best to write in English. I might write in Chinese if I really want to write something. I used MS SQLServer a few years ago. And I found that MySQL is very alike SQLServer. The … More Start MySQL server