Trie data structure: 425 Word square

 Here is the gist. 

Ideally it should take me less than 10 minutes to come out Trie data structure with design, and then go over depth first search, word by word, each word should consider if the first few chars ( 0 - level - 1) should be fixed, which can be looked up in ith column, i's value is level. 

When I worked on my first practice yesterday, I did not come out the clear idea illustrated in the following graph. It should be really simple and straightforward. 

Here are some highlights: