假设有12个初始归并段，其长度分别为85，68，62，9，18，60，20，3，6，8，44，30；现要进行4路外部归并排序，试画出表示归并过程的最佳归并树，并计算树的带权路径长度WPL。
参考答案：应加4-(12-1)mod(4-1)-1=1个虚段。
WPL=(3+6+8)×3+(9+18+20+30+44+60+62)×2+(68+85)×1=690
解析： 如何判定附加虚段的数目呢一般情况下，对k路归并而言，容易推导到。若(m-1)mod(k-1)=0，则不需要附加虚段，否则需要附加k-(m-1)rood(k-1)-1个虚段。换句话说，第一次归并为(m-1)rood(k-1)+1个路归并。其中mod表示求模运算符。
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| Most adults once studied at school, had classes and did homework every day. The same 1 is going on at school now. 2 it seems that doing weekend homework is 3 problem for the modern students. All the students should agree that weekend homework should be abolished (取消). It′s 4 for them studying at school five days a week. They have a lot of interests. With homework to do on Saturday and Sunday, when can they find 5 to help around the house, go and see a football or basketball game or a good film, join in family recreations (娱乐), or just have 6 at home? Because of these other activities, the homework can not be finished until 7 . So their weekend homework is usually done in such a hurry that on Monday the 8 teachers often threaten (威胁)to fail whole class of students because they know nothing about the 9 . If there were no weekend homework for the students to do, they would be happy to school on Monday 10 having a good rest and to learn what the teachers teach. | ||||
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