island count follow up No. 1

island count follow up No 1

Follow-up 1:
Let's say the dataset is very large.
The input data is now a list of coordinates for any piece of land.
No guarantee on order of coordinates given to you.  (random order)

(1000, 23)
(0, 1)
(0, 3)(3948, 1837)

Julia's analysis:

size k -> preprocessing size k -> order by sort by row, second col (added after mock interview, I did say that 
it is not necessary)

put all cordination into dictionary to loop up O(1) <- 
key = row + ';' + col -> 1 -> value 1's dictionary -> O(1)

visited one -> look up hashset O(1)


1st loop:  insert all into land_dictionary
2nd loop:  lookup neighbors in land_dcitionary and mark in visisted dictionary

returning number of island at the very end