[depth first search notes] Abstract DFS

abstract dfs No graph exists , But you can build an abstract diagram based on the state , The vertex on the graph is a state ,

The subtree corresponding to each state , Is the state that can be achieved by searching .

The edge on the graph is the transition relationship between States （ Further search / to flash back ）

We can argue that , once dfs In fact, I completed a depth first search on the search tree