17 If an undirected graph with n nodes and k edges is a forest (n>k), then there must be ( ) trees in the forest.
查看答案
18 A and B are two nodes on a binary tree. In the in-order traversal, the condition for A before B is ( ).
A is to the left of B
B. A is to the right of B
C. A is the ancestor of B
D. A is a descendant of B
19 After converting a tree into a binary tree, the shape of the binary tree is ( ).
A. Only
B. There are many
C. There are many, but none of the root nodes have left children
D. There are many, but none of the root nodes have right children
20 Which of the following statements is correct ().
A. There are at most two subtrees in a binary tree, and there are left and right subtrees
B. A binary tree is an ordered tree of degree 2
C. There is no left-right distinction when the node has only one child in a binary tree.
D. There must be a node of degree 2 in the binary tree
21 There are altogether ( ) binary trees with 7 nodes, and they are not similar to each other.
A. 429
B. 428
C. 427
D. 426
微信支付 
支付宝支付