对序列(70，75，82，90，23，16)用快速排序方法进行排序，以序列的第一个元素为划分的基准。在第一趟划分后数据元素的排列是( )。
A．16，75，82，90，23，70
B．16，70，82，90，23，75
C．16，23，70，90，82，75
D．16，23，82，90，70，75
参考答案：C
解析： 快速排序元素划分的方法是：在右端遇到比基准元素小的元素，则与基准元素交换位置，然后从左端开始比较；遇到比基准元素大的元素，与基准元素交换位置，再从右端继续比较，直到与所有元素比较一次，此时完成一次划分。本题中进行快速排序时元素的移动如图20-16所示。可知，当完成一趟排序后的序列是16，23，70，90，82， 75。即选项C是正确答案。
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| Jane raced onto the train platform and asked a porter, "Is this the train to Rochester?" "Yes," said the porter, "but only the Hey! Wait." He was too 1 . Jane had raced off 2 he had finished speaking. She had just 3 herself in  a seat when the train 4 out of the station. Jane got out her book and settled down to read. After about an hour or so, she looked 5 and glanced out of the window. "That's 16 ." she thought. "the landscape(景色)doesn't look 7 ,and it should; I've 8 this route so many times." She was getting 9 when the big, red-faced conductor walked up and asked for her 10 . One glance was enough. He 11 his head in friendly reproach(责备) and said, "Now, young lady, what did you do a fool thing like that for? This is the 12 ticket. You 13 have sat at the back of the train. The Rochester-bound(开往) section was 14 at the last station.  Jane's face grew red. "I'm sorry," she said, "I guess I was in too much of a 15 to find out…"Well," said the conductor, "don't 16 . You shouldn't have been in such a hurry, but I dare say we can 17 you a train going in the right 18 at Syracuse. You'll be a couple of hours late 19 , though." When Jane finally stepped onto the Rochester platform, her mother 20 up to her . "Oh, Jane, we have been so worried. What on earth happened?" "Well, Mom," said Jane, "it's a long story......." | ||||
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