Breadth-First Search

Color

• white: 未被发现/访问
• gray: 已被发现(进入队列), 邻接结点未全部发现
• black: 已被发现, 邻接结点全部发现

Parent

广度优先树父结点

Distance

距离 = v.pi.d + 1

Queue

Using mark array and queue:

• Shortest Paths.
• Diameter of Tree (树直径): two pass for BFS.