Connected Component

• Connected is usually associated with undirected graphs (two way edges): there is a path between every two nodes.

• Strongly connected is usually associated with directed graphs (one way edges): there is a route between every two nodes.

• Complete graphs are undirected graphs where there is an edge between every pair of nodes.

• 检查directed graph是否有环可以用DFS或者BFS(course schedule)

• 检查undirected graph 是否有环可以用Union Find