# Graph 圖形
* explore a graph
Such like we want to find the path between two nodes in the grpah.
## 1. Definition
#### Recall graph G = (V, E)
* V = set of vertices (arbitrary labels)
* E = set of edges i.e. vertex pairs (v, w)
* ordered pair ⇒ directed edge of grap 有向圖
* unordered pair ⇒ undirected 無向圖

* Self loop and self edge is not permittrd

#### Degree
* Degree of vertex v:
* **undriected gra