问题 单项选择题

拓扑序列是无环有向图中所有顶点的一个线性序列,图中任意路径中的各个顶点在该图的拓扑序列中保持先后关系。对于图6-10所示的有向图,()不是其的一个拓扑序列。

A.1526374

B.1526734

C.5123764

D.5126374

答案

参考答案:C

解析:

[要点解析] 拓扑序列是将有向图中所有顶点的一个线性序列的过程,并且该序列满足:若在图中存在从顶点Vi到Vj有一条路径,则在该线性序列中,顶点Vi必然在顶点Vj之前。

对有向图进行拓扑排序的方法如下:

①在有向图中选择一个入度为零(没有前驱)的顶点且输出之。

②从网中删除该顶点及从该顶点出发的所有弧。

③重复上述两步,直到图中不存在入度为0的顶点为止。

对于图6-10所示的有向图,进行拓扑排序的顶点序列有:5126374、5126734、1526374、1526734。而选项C的“5123764”不是其的一个拓扑序列。

单项选择题
阅读理解

阅读理解.

     Ladies and Gentlemen, some strange, wild and wonderful stories colored the news in 2010,

you may like them.

     ★A Copenhagen bus company has put "love seats" on 103 of its buses for people looking

for a partner. "Even love at first sight is possible on the bus," said a spokesman for the

company to explain the two seats on each bus that are covered in red cloth and a "love

seat" sign.

     ★Shoppers at an international luxury fair in Italy, found a cell-phone-equipped golden

coffin among the items on display. The phones will help "the dead" contact relatives if they

have been buried alive by mistake.

     ★A man in New York came up with a disarming(手无寸铁的)way to perform his

latest bank heist , approaching the clerk's window with a large bunch of flowers and handing

over a note saying "give me the money!"

     ★An Englishman who lost all his legs and arms in an electrical accident successfully

swam across the Channel, a challenge he had been preparing for two years. The whole

cost is 400 dollars. 

     ★A set of artificial teeth(假牙) made for Britain's war-time prime minister Winston

Churchill known as "the teeth that saved the world" sold for nearly 18,000 pounds (21,500

euros, 24,000 dollars) at auction(拍卖).

     ★A British woman caused an Internet hate campaign after she was caught on camera

dumping(抛弃)a cat in a rubbish bin. She was fined 250 pounds (400 dollars, 280 euros)

after pleading guilty.

     ★The BBC apologized completely and without any doubts after a radio presenter

jokingly announced that Queen Elizabeth II had died.

     ★Two Australian men needed surgery(手术)after shooting each other in the bottoms

during a drinking session to see if it would hurt and they were charged 400 dollars separately.

     ★A Kuwaiti MP(议员) suggested state-aid for male citizens to take second wives, in

an effort to reduce the large number of unmarried women in the oil-rich state.

1.What is special about the coffin in the second news?

A. It is golden.

B. It has a cell phone.

C. It is new.

D. It has many items.

2.What is the probable meaning of the underlined word "heist" in the third news?

A. robbery

B. love

C. discussion

D. repair

3.Who has to spend 400 dollars to do the surgery?

A. A British woman who dumped a cat in a rubbish bin.

B. One who bought Winston Churchill's artificial teeth.

C. An Australian man who was shot in bottom to test the hurt.

D. An Englishman crossing the Channel without legs and arms.

4.From the last news we can infer that _________.

A. In Kuwait many men are eager to get married

B. A lot of rich single men lived in Kuwait

C. There are quantities of oil in Kuwait

D. There are many single women in Kuwait