Algorithmic questions about trees

ppxlqq

Given a tree


(0,1)
(0,7)
(0,12)
(0,13)
(0,15)
(1,2)
(1,4)
(1,6)
(1,7)
(2,3)
(2,5)
(2,6)
(3,4)
(3,5)
(7,8)
(8,9)
(8,10)
(8,11)
(9,10)
(9,11)
(12,13)
(13,14)
(13,15)


0 represents the root node, and each array represents whether there are directed edges between the two nodes. How do I tell if a node is the ancestor of another node? Thank you

ank11111

Consider these questions:
1, How do you represent a single Node in the Graph?
2, How do you represent a single edge in the Graph?
3, How do you build the Graph from your input?

If there is a path from Node A to Node B, then A is a ancestor of B.

ppxlqq

However, in my algorithm book, in a tree rooted at r, if the vertex v is on a unique path T from vertex w to r, v is the ancestor of w

The key here is the only path I don't know how to deal with, thank you!

ank11111

If it is a tree, the path should be unique. If it is a graph, the path is not necessarily unique.

If each of your nodes knows their dad, then start from w, go to w dad, then w grandpa, ..., until r. If you meet v in the middle, then v is the ancestor of w.

wanwei

1. Deep search
2. Minimal transitive closure algorithm
3. Find the shortest path between two points, true if it is not infinite

mtss123

// record the input pairs.

boolean isAncestor(int a,int b){
  // judge if a is ancestor of b.
  // travel from b to 0
  // return if a is visted
}