JAVA数据结构习题及解答(英)

QuestionsThese questions are intended as a self-test for readers.Answers to the questions may be found in Appendix C.1.In many data structures you can________a single record,_________it,and_______it.2.Rearranging the contents of a data structure into a certain order is called_________.30CHAPTER1Overview3.In a database,a field isa.a specific data item.b.a specific object.c.part of a record.d.part of an algorithm.4.The field used when searching for a particular record is the______________.5.In object-oriented programming,an objecta.is a class.b.may contain data and methods.c.is a program.d.may contain classes.6.A classa.is a blueprint for many objects.b.represents a specific real-world object.c.will hold specific values in its fields.d.specifies the type of a method.7.In Java,a class specificationa.creates objects.b.requires the keyword new.c.creates references.d.none of the above.8.When an object wants to do something,it uses a________.9.In Java,accessing an object’s methods requires the_____operator.10.In Java,boolean and byte are_____________.(There are no experiments or programming projects for Chapter1.)Questions31Chapter1,OverviewAnswers to Questions1.insert,search for,delete2.sorting3.c4.search key5.b6.a7.d8.method9.dot10.data typesQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.Inserting an item into an unordered arraya.takes time proportional to the size of the array.b.requires multiple comparisons.c.requires shifting other items to make room.d.takes the same time no matter how many items there are.2.True or False:When you delete an item from an unordered array,in most cases you shift other items to fill in the gap.3.In an unordered array,allowing duplicatesa.increases times for all operations.b.increases search times in some situations.c.always increases insertion times.d.sometimes decreases insertion times.4.True or False:In an unordered array,it’s generally faster to find out an item is not in the array than to find out it is.5.Creating an array in Java requires using the keyword________.6.If class A is going to use class B for something,thena.class A’s methods should be easy to understand.b.it’s preferable if class B communicates with the program’s user.c.the more complex operations should be placed in class A.d.the more work that class B can do,the better.7.When class A is using class B for something,the methods and fields class A can access in class B are called class B’s__________.74CHAPTER2Arrays8.Ordered arrays,compared with unordered arrays,area.much quicker at deletion.b.quicker at insertion.c.quicker to create.d.quicker at searching.9.A logarithm is the inverse of_____________.10.The base10logarithm of1,000is_____.11.The maximum number of elements that must be examined to complete a binary search in an array of200elements isa.200.b.8.c.1.d.13.12.The base2logarithm of64is______.13.True or False:The base2logarithm of100is2.14.Big O notation tellsa.how the speed of an algorithm relates to the number of items.b.the running time of an algorithm for a given size data structure.c.the running time of an algorithm for a given number of items.d.how the size of a data structure relates to the number of items.15.O(1)means a process operates in_________time.16.Either variables of primitive types or_________can be placed in an array. Chapter2,ArraysAnswers to Questions1.d2.True3.b4.False5.new6.d740APPENDIX C Answers to Questions7.interface8.d9.raising to a power10.311.812.613.False14.a15.constant16.objectsuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.puter sorting algorithms are more limited than humans in thata.humans are better at inventing new algorithms.puters can handle only a fixed amount of data.c.humans know what to sort,whereas computers need to be told.puters can compare only two things at a time.2.The two basic operations in simple sorting are_________items and_________ them(or sometimes_________them).3.True or False:The bubble sort always ends up comparing every item with every other item.4.The bubble sort algorithm alternates betweenparing and swapping.b.moving and copying.c.moving and comparing.d.copying and comparing.5.True or False:If there are N items,the bubble sort makes exactly N*N comparisons.Questions1096.In the selection sort,a.the largest keys accumulate on the left(low indices).b.a minimum key is repeatedly discovered.c.a number of items must be shifted to insert each item in its correctlysorted position.d.the sorted items accumulate on the right.7.True or False:If,in a particular sorting situation,swaps take much longer than comparisons,the selection sort is about twice as fast as the bubble sort.8.A copy is________times as fast as a swap.9.What is the invariant in the selection sort?10.In the insertion sort,the“marked player”described in the text corresponds to which variable in the insertSort.java program?a.inb.outc.tempd.a[out]11.In the insertion sort,“partially sorted”means thata.some items are already sorted,but they may need to be moved.b.most items are in their final sorted positions,but a few still need to be sorted.c.only some of the items are sorted.d.group items are sorted among themselves,but items outside the groupmay need to be inserted in it.12.Shifting a group of items left or right requires repeated__________.13.In the insertion sort,after an item is inserted in the partially sorted group,it willa.never be moved again.b.never be shifted to the left.c.often be moved out of this group.d.find that its group is steadily shrinking.110CHAPTER3Simple Sorting14.The invariant in the insertion sort is that________.15.Stability might refer toa.items with secondary keys being excluded from a sort.b.keeping cities sorted by increasing population within each state,in a sortby state.c.keeping the same first names matched with the same last names.d.items keeping the same order of primary keys without regard to secondary keys.Chapter3,Simple SortingAnswers to Questions1.dparing and swapping(or copying)3.False4.a5.False6.b7.False8.three9.Items with indices less than or equal to outer are sorted.10.c11.d12.copies13.b14.Items with indices less than outer are partially sorted.15.buestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.Suppose you push10,20,30,and40onto the stack.Then you pop three items. Which one is left on the stack?2.Which of the following is true?a.The pop operation on a stack is considerably simpler than the remove operation on a queue.b.The contents of a queue can wrap around,while those of a stack cannot.c.The top of a stack corresponds to the front of a queue.d.In both the stack and the queue,items removed in sequence are takenfrom increasingly high index cells in the array.3.What do LIFO and FIFO mean?4.True or False:A stack or a queue often serves as the underlying mechanism on which an ADT array is based.5.Assume an array is numbered with index0on the left.A queue representing a line of movie-goers,with the first to arrive numbered1,has the ticket window on the right.Thena.there is no numerical correspondence between the index numbers andthe movie-goer numbers.b.the array index numbers and the movie-goer numbers increase inopposite left-right directions.c.the array index numbers correspond numerically to the locations in theline of movie-goers.d.the movie-goers and the items in the array move in the same direction.6.As other items are inserted and removed,does a particular item in a queue move along the array from lower to higher indices,or higher to lower?7.Suppose you insert15,25,35,and45into a queue.Then you remove three items.Which one is left?8.True or False:Pushing and popping items on a stack and inserting and removing items in a queue all take O(N)time.174CHAPTER4Stacks and Queues9.A queue might be used to holda.the items to be sorted in an insertion sort.b.reports of a variety of imminent attacks on the star ship Enterprise.c.keystrokes made by a computer user writing a letter.d.symbols in an algebraic expression being evaluated.10.Inserting an item into a typical priority queue takes what big O time?11.The term priority in a priority queue means thata.the highest priority items are inserted first.b.the programmer must prioritize access to the underlying array.c.the underlying array is sorted by the priority of the items.d.the lowest priority items are deleted first.12.True or False:At least one of the methods in the priorityQ.java program (Listing4.6)uses a linear search.13.One difference between a priority queue and an ordered array is thata.the lowest-priority item cannot be extracted easily from the array as it can from the priority queue.b.the array must be ordered while the priority queue need not be.c.the highest priority item can be extracted easily from the priority queue but not from the array.d.All of the above.14.Suppose you based a priority queue class on the OrdArray class in the orderedArray.java program(Listing2.4)in Chapter2,“Arrays.”This will buy you binary search capability.If you wanted the best performance for your priority queue,would you need to modify the OrdArray class?15.A priority queue might be used to holda.passengers to be picked up by a taxi from different parts of the city.b.keystrokes made at a computer keyboard.c.squares on a chessboard in a game program.d.planets in a solar system simulation.Chapter4,Stacks and QueuesAnswers to Questions1.102.bst-In-First-Out;and First-In-First-Out4.False.It’s the other way around.5.b6.It doesn’t move at all.7.458.False.They take O(1)time.9.c10.O(N)11.c12.True13.b14.Yes,you would need a method to find the minimum value.15.aQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.Questions2451.Which of the following is not true?A reference to a class objecta.can be used to access public methods in the object.b.has a size dependant on its class.c.has the data type of the class.d.does not hold the object itself.2.Access to the links in a linked list is usually through the_________link.3.When you create a reference to a link in a linked list,ita.must refer to the first link.b.must refer to the link pointed to by current.c.must refer to the link pointed to by next.d.can refer to any link you want.4.How many references must you change to insert a link in the middle of a singly linked list?5.How many references must you change to insert a link at the end of a singly linked list?6.In the insertFirst()method in the linkList.java program(Listing5.1),the statement newLink.next=first;means thata.the next new link to be inserted will refer to first.b.first will refer to the new link.c.the next field of the new link will refer to the old first link.d.newLink.next will refer to the new first link in the list.7.Assuming current points to the next-to-last link in a singly linked list,what statement will delete the last link from the list?8.When all references to a link are changed to refer to something else,what happens to the link?9.A double-ended lista.can be accessed from either end.b.is a different name for a doubly linked list.c.has pointers running both forward and backward between links.d.has its first link connected to its last link.246CHAPTER5Linked Lists10.A special case often occurs for insertion and deletion routines when a list is ________.11.Assuming a copy takes longer than a comparison,is it faster to delete an item with a certain key from a linked list or from an unsorted array?12.How many times would you need to traverse a singly linked list to delete the item with the largest key?13.Of the lists discussed in this chapter,which one would be best for implementing a queue?14.Which of the following is not true?Iterators would be useful if you wanted toa.do an insertion sort on a linked list.b.insert a new link at the beginning of a list.c.swap two links at arbitrary locations.d.delete all links with a certain key value.15.Which do you think would be a better choice to implement a stack:a singly linked list or an array?Chapter5,Linked ListsAnswers to Questions1.b2.first3.d4.25.16.c7.current.next=null;8.Java’s garbage collection process destroys it.Chapter5,Linked Lists7419.a10.empty11.a linked list12.once,if the links include a previous reference13.a double-ended list14.bually,the list.They both do push()and pop()in O(1)time,but the list uses memory more efficiently.QuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.If the user enters10in the triangle.java program(Listing6.1),what is the maximum number of“copies”of the triangle()method(actually just copies of its argument)that exist at any one time?2.Where are the copies of the argument,mentioned in question1,stored?a.in a variable in the triangle()methodb.in a field of the TriangleApp classc.in a variable of the getString()methodd.on a stack3.Assume the user enters10as in question1.What is the value of n when the triangle()method first returns a value other than1?4.Assume the same situation as in question1.What is the value of n when the triangle()method is about to return to main()?5.True or false:In the triangle()method,the return values are stored on thestack.6.In the anagram.java program(Listing6.2),at a certain depth of recursion,a version of the doAnagram()method is working with the string“led”.When this method calls a new version of itself,what letters will the new version be working with?7.We’ve seen that recursion can take the place of a loop,as in the loop-oriented orderedArray.java program(Listing2.4)and the recursive binarySearch.java program(Listing6.3).Which of the following is not true?a.Both programs divide the range repeatedly in half.b.If the key is not found,the loop version returns because the rangebounds cross,but the recursive version occurs because it reaches thebottom recursion level.c.If the key is found,the loop version returns from the entire method, whereas the recursive version returns from only one level of recursion.d.In the recursive version the range to be searched must be specified in the arguments,while in the loop version it need not be.310CHAPTER6Recursion8.In the recFind()method in the binarySearch.java program(Listing6.3),what takes the place of the loop in the non-recursive version?a.the recFind()methodb.arguments to recFind()c.recursive calls to recFind()d.the call from main()to recFind()9.The binarySearch.java program is an example of the_________approach to solving a problem.10.What gets smaller as you make repeated recursive calls in the redFind() method?11.What becomes smaller with repeated recursive calls in the towers.java program (Listing6.4)?12.The algorithm in the towers.java program involvesa.“trees”that are data storage devices.b.secretly putting small disks under large disks.c.changing which columns are the source and destination.d.moving one small disk and then a stack of larger disks.13.Which is not true about the merge()method in the merge.java program(Listing6.5)?a.Its algorithm can handle arrays of different sizes.b.It must search the target array to find where to put the next item.c.It is not recursive.d.It continuously takes the smallest item irrespective of what array it’s in.14.The disadvantage of mergesort is thata.it is not recursive.b.it uses more memory.c.although faster than the insertion sort,it is much slower than quicksort.d.it is complicated to implement.15.Besides a loop,a___________can often be used instead of recursion. Chapter6,RecursionAnswers to Questions1.102.d3.24.105.false6.“ed”7.b8.c9.divide-and-conquer10.the range of cells to search11.the number of disks to transfer12.c13.b14.b15.stackQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.The Shellsort works bya.partitioning the array.b.swapping adjacent elements.c.dealing with widely separated elements.d.starting with the normal insertion sort.2.If an array has100elements,then Knuth’s algorithm would start with an interval of________.Questions3613.To transform the insertion sort into the Shellsort,which of the following do you not do?a.Substitute h for1.b.Insert an algorithm for creating gaps of decreasing width.c.Enclose the normal insertion sort in a loop.d.Change the direction of the indices in the inner loop.4.True or false:A good interval sequence for the Shellsort is created by repeatedly dividing the array size in half.5.Fill in the big O values:The speed of the Shellsort is more than_______but less than________.6.Partitioning isa.putting all elements larger than a certain value on one end of the array.b.dividing an array in half.c.partially sorting parts of an array.d.sorting each half of an array separately.7.When partitioning,each array element is compared to the_______.8.In partitioning,if an array element is equal to the answer to question7,a.it is passed over.b.it is passed over or not,depending on the other array element.c.it is placed in the pivot position.d.it is swapped.9.True or false:In quicksort,the pivot can be an arbitrary element of the array.10.Assuming larger keys on the right,the partition isa.the element between the left and right subarrays.b.the key value of the element between the left and right subarrays.c.the left element in the right subarray.d.the key value of the left element in the right subarray.11.Quicksort involves partitioning the original array and then_________.362CHAPTER7Advanced Sorting12.After a partition in a simple version of quicksort,the pivot may beed to find the median of the array.b.exchanged with an element of the right subarray.ed as the starting point of the next partition.d.discarded.13.Median-of-three partitioning is a way of choosing the_______.14.In quicksort,for an array of N elements,the partitionIt()method will examine each element approximately______times.15.True or false:You can speed up quicksort if you stop partitioning when the partition size is5and finish by using a different sort.Chapter7,Advanced SortingAnswers to Questions1.c2.403.d4.false5.O(N*logN),O(N2)6.a7.pivot8.d9.true10.c11.partitioning the resulting subarrays12.b13.pivot14.log2N15.trueQuestionsThese questions are intended as a self-test for readers.Answers may be found inAppendix C.1.Insertion and deletion in a tree require what big O time?2.A binary tree is a search tree ifa.every non-leaf node has children whose key values are less than(or equalto)the parent.b.every left child has a key less than the parent and every right child has akey greater than(or equal to)the parent.c.in the path from the root to every leaf node,the key of each node isgreater than(or equal to)the key of its parent.d.a node can have a maximum of two children.3.True or False:Not all trees are binary trees.4.In a complete binary tree with20nodes,and the root considered to be at level 0,how many nodes are there at level4?5.A subtree of a binary tree always hasa.a root that is a child of the main tree’s root.b.a root unconnected to the main tree’s root.c.fewer nodes than the main tree.d.a sibling with the same number of nodes.6.In the Java code for a tree,the______and the_______are generally separate classes.Questions4237.Finding a node in a binary search tree involves going from node to node, askinga.how big the node’s key is in relation to the search key.b.how big the node’s key is compared to its right or left children.c.what leaf node we want to reach.d.what level we are on.8.An unbalanced tree is onea.in which most of the keys have values greater than the average.b.whose behavior is unpredictable.c.in which the root or some other node has many more left children thanright children,or vice versa.d.that is shaped like an umbrella.9.Inserting a node starts with the same steps as_______a node.10.Suppose a node A has a successor node S.Then S must have a key that is larger than_____but smaller than or equal to_______.11.In a binary tree used to represent a mathematical expression,which of the following is not true?a.Both children of an operator node must be operands.b.Following a postorder traversal,no parentheses need to be added.c.Following an inorder traversal,parentheses must be added.d.In pre-order traversal a node is visited before either of its children.12.If a tree is represented by an array,the right child of a node at index n has an index of_______.13.True or False:Deleting a node with one child from a binary search tree involves finding that node’s successor.14.A Huffman tree is typically used to_______text.15.Which of the following is not true about a Huffman tree?a.The most frequently used characters always appear near the top of the tree.b.Normally,decoding a message involves repeatedly following a path fromthe root to a leaf.424CHAPTER8Binary Treesc.In coding a character you typically start at a leaf and work upward.d.The tree can be generated by removal and insertion operations on apriority queue.Chapter8,Binary TreesAnswers to Questions1.O(logN)2.b3.True4.55.c6.node,tree7.a8.cChapter8,Binary Trees7439.finding10.A,A’s left-child descendents11.d12.2*n+113.Falsepress15.cQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.A2-3-4tree is so named because a node can havea.three children and four data items.b.two,three,or four children.c.two parents,three children,and four items.d.two parents,three items,and four children.2.A2-3-4tree is superior to a binary search tree in that it is________.3.Imagine a parent node with data items25,50,and75.If one of its child nodes had items with values60and70,it would be the child numbered__________.4.True or False:Data items are located exclusively in leaf nodes.514CHAPTER102-3-4Trees and External Storage5.Which of the following is not true each time a node is split?a.Exactly one new node is created.b.Exactly one new data item is added to the tree.c.One data item moves from the split node to its parent.d.One data item moves from the split node to its new sibling.6.A2-3-4tree increases its number of levels when________.7.Searching a2-3-4tree does not involvea.splitting nodes on the way down if necessary.b.picking the appropriate child to go to,based on data items in a node.c.ending up at a leaf node if the search key is not found.d.examining at least one data item in any node visited.8.After a non-root node of a2-3-4tree is split,does its new right child contain the item previously numbered0,1,or2?9.A4-node split in a2-3-4tree is equivalent to a_______in a red-black tree.10.Which of the following statements about a node-splitting operation in a2-3 tree(not a2-3-4tree)is not true?a.The parent of a split node must also be split if it is full.b.The smallest item in the node being split always stays in that node.c.When the parent is split,child2must always be disconnected from itsold parent and connected to the new parent.d.The splitting process starts at a leaf and works upward.11.What is the big O efficiency of a2-3tree?12.In accessing data on a disk drive,a.inserting data is slow but finding the place to write data is fast.b.moving data to make room for more data is fast because so many items can be accessed at once.c.deleting data is unusually fast.d.finding the place to write data is comparatively slow but a lot of data can be written quickly.13.In a B-tree each node contains_______data items.Questions51514.True or False:Node splits in a B-tree have similarities to node splits in a2-3 tree.15.In external storage,indexing means keeping a file ofa.keys and their corresponding blocks.b.records and their corresponding blocks.c.keys and their corresponding records.st names and their corresponding keys.Chapter9,Red-Black TreesAnswers to Questions1.in order(or inverse order)2.b3.False4.d5.b6.rotations,changing the colors of nodes7.red8.a9.left child,right child10.d11.a node,its two children12.b13.True14.a15.TrueQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.574CHAPTER11Hash Tablesing big O notation,say how long it takes(ideally)to find an item in a hash table.2.A__________transforms a range of key values into a range of index values.3.Open addressing refers toa.keeping many of the cells in the array unoccupied.b.keeping an open mind about which address to use.c.probing at cell x+1,x+2,and so on until an empty cell is found.d.looking for another location in the array when the one you want is occupied.ing the next available position after an unsuccessful probe is called_____________.5.What are the first five step sizes in quadratic probing?6.Secondary clustering occurs becausea.many keys hash to the same location.b.the sequence of step lengths is always the same.c.too many items with the same key are inserted.d.the hash function is not perfect.7.Separate chaining involves the use of a_____________at each location.8.A reasonable load factor in separate chaining is________.9.True or False:A possible hash function for strings involves multiplying each character by an ever-increasing power.10.The best technique when the amount of data is not well known isa.linear probing.b.quadratic probing.c.double hashing.d.separate chaining.11.If digit folding is used in a hash function,the number of digits in each group should reflect_____________.12.True or False:In linear probing an unsuccessful search takes longer than a successful search.Questions57513.In separate chaining the time to insert a new itema.increases linearly with the load factor.b.is proportional to the number of items in the table.c.is proportional to the number of lists.d.is proportional to the percentage of full cells in the array.14.True or False:In external hashing,it’s important that the records don’t become full.15.In external hashing,all records with keys that hash to the same value are located in___________.Chapter11,Hash TablesAnswers to Questions1.O(1)2.hash function3.d4.linear probing5.1,4,9,16,256.b7.linked listChapter11,Hash Tables7458.1.09.True10.d11.the array size12.False13.a14.False15.the same blockQuestionsThese questions are intended as a self-test for readers.Answers may be found in Appendix C.1.What does the term complete mean when applied to binary trees?a.All the necessary data has been inserted.b.All the rows are filled with nodes,except possibly the bottom one.c.All existing nodes contain data.d.The node arrangement satisfies the heap condition.2.What does the term weakly ordered mean when applied to heaps?3.A node is always removed from the__________.4.To“trickle up”a node in a descending heap meansa.to repeatedly exchange it with its parent until it’s larger than its parent.b.to repeatedly exchange it with its child until it’s larger than its child.c.to repeatedly exchange it with its child until it’s smaller than its child.d.to repeatedly exchange it with its parent until it’s smaller than its parent.5.A heap can be represented by an array because a heap。