Leetcode patterns- DFS

After 1000 medium level problems. write down the patterns what i have learned .

I have been started on leetcode since end of 2020 . Until Jan 2022 I have done enough problems and should have a break to write down what i have learned, now i am at 1004th problem .

There are a few patterns be identified when solving the problems, I want to share all these patterns also with some high ranking medium leetcode problems to you , beside the problems itself, more important is to master the nice algorithm ideas used in real projects.

Why medium level ? they are more likely matched with the difficulty level of either interview problems or real projects problems . in short, if you are not beginner (or you are, but after trying 10–20 easy ones you will want to medium) or ACM competition, medium level is best .

This is the 1st one — Depth First Search

Core idea

def dfs(input, visited): 
     if stop_condition or visited:
          return information to parent
     next_inputs = get_next_inputs()
     for next_input in next_inputs:
         visited |= current
         res = dfs(next_input, visited)
         # visited -= {current}  depends, some issue need to restore the search state
      return information needed by parent

so the idea is very simple. pass in whatever needed , check stop_condition (this should be the first thing for every recursive function), save into visited if needed and get next states…