Lab 5 Sorting with Linked Lists

Transcription

1 UNIVERSITY OF CALIFORNIA, SANTA CRUZ BOARD OF STUDIES IN COMPUTER ENGINEERING CMPE13/L: INTRODUCTION TO PROGRAMMING IN C WINTER 2013 Lab 5 Srting with Linked Lists Intrductin Reading This lab intrduces the cncept f pinters, bth t data and functins, thrugh the cncept f a dubly-linked list data structure. This is a very cmmn structure that is used in many prgrams fr string expandable lists f rdered data. Yu will als be given a functin t initialize a list f unsrted data, in which yu will need t srt and create an algrithm t cunt reccurrences f data stred in the items. Yu will be implementing a generic LinkedList library that can stre, srt, and print any type f data. Once that library is cmplete yu will use an existing linked list that I have created fr yu (alng with the element-wise PrintWrd() and CmpareWrd() functins) t write cde that srts a linked list cntaining wrds and then implement a wrd-cunt functin that perates n a srted list. I have prvided cde that creates a list and des a wrd cunt n it, but it assumes that the list is unrdered. Yu will need t write a wrd cunting algrithm that is faster than the ne prvided t yu (which is pssible as yu knw the list is already srted). K&R chapter 5, 6.7, 7.8.5, appendix B5 Cncepts Dubly-Linked List Memry Allcatin Srting Pinters incl. NULL & functin pinters Algrithmic Cmparisns Prvided files srt.c cntains: main() which cntains sme Starter Cde that initializes an unsrted list f wrds, prints it ut, and cunts reccurrences f wrds. Yu are t cmplete main() t srt that list, print ut the srted versin and then design and implement an algrithm t cunt the ccurrences f wrds that is mre efficient than the unsrted algrithm (remember

2 that this algrithm has the knwledge that the list is presrted befre it is given). The functins used t implement the starter cde are given belw main() with cmments t dcument their functinality. There is als a specified place t define a SrtedWrdCunt() functin. This functin WILL NOT COMPILE unless yu have cmpleted implementing the LinkedList library. D nt deal with the srting part until yu have cmpleted (implemented and tested) the library. LinkedList.h prvides #define cnstants fr return values alng with the functin prttypes that yu will be implementing. Cmments abve the functin prttypes describe their functinality. D nt cpy this whle file when creating LinkedList.c, just cpy the individual functin prttypes. Cmmn.h Includes the standard fixed-width and Blean data types. Als prvides errr return values. Data.h this cntains the functin prttype f the functin that generates the data fr the given unsrted wrd list. This header file has already been included fr yu within srt.c. Data.a this is a precmpiled library file that generates the data fr the given unsrted wrd list. Just include this file within yur prject via Run Set Prject Cnfiguratin Custmize Cnf: [default] Libraries Add Library/Object File. Assignment requirements Fr this lab yu are required t make a detailed iterative-design plan. Yu must have this dne and available t shw the TAs/tutrs befre they ll answer any cde related questins. If yu are unsure f what yurs shuld lk like, please ask befre yu start cding as fllwing yur plan will save yu bth time and lst pints. Yur prgram will implement the functins whse prttypes are prvided in LinkedList.h. The functins all have apprpriate dcumentatin and describe the required functinality. Within srt.c yu will: Create a new algrithm fr cunting ccurrences f wrds within a functin named SrtedWrdCunt() (whse definitin fllws frm UnsrtedWrdCunt()) that uses the knwledge that it s prcessing a presrted wrd list t be mre efficient than UnsrtedWrdCunt(). Yu shuld first read and understand hw UnsrtedWrdCunt() wrks befre attempting t write SrtedWrdCunt() s that yu can be sure that yurs is faster. T think f hw fast an algrithm is, just cnsider hw many times it accesses each element in the list.

3 Print ut the data array alng with the array f ccurrences fund using yur new SrtedWrdCunt() functin. The cmplete utput when the prgram is run shuld be tw sets f the array printed alng with its wrd cunt. Check the Expected Output sectin f this lab. Once the necessary utput is displayed, yu will free up all f the memry used by the linked list. Yu SHOULD NOT free the data cntained within each linked list item. BE CAREFUL HERE: it is nt safe t try t use data after it has been free()d and yu will nt get the pints if yu d. Add inline cmments t explain yur cde (abut 1 cmment every 6 lines f cde is prbably right). Create a readme file named README.txt cntaining the fllwing items. Spelling and grammar cunt as part f yur grade s yu'll want t prf-read this befre submitting. This will fllw the same rugh utline as a lab reprt fr a regular science class. It shuld be n the rder f three paragraphs with several sentences in each paragraph. First yu shuld list yur name & the names f clleagues wh yu have cllabrated with. NOTE: cllabratin!= cpying In the next sectin yu shuld prvide a summary f the lab in yur wn wrds. Highlight what yu thught were the imprtant aspects f the lab. If these differ frm hw the lab manual presents things, make a nte f that. The fllwing sectin shuld describe yur apprach t the lab. What was yur general apprach t the lab? Did yu read the manual first r what were yur first steps? What went wrng as yu wrked thrugh it? What wrked well? Hw wuld yu apprach this lab differently if yu were t d it again? Did yu wrk with anyne else in the class? Hw did yu wrk with them and what did yu find helpful/unhelpful? The final sectin shuld describe the results f yu implementing the lab. Hw did it end up finally? Hw many hurs did yu end up spending n it? What'd yu like abut it? What did yu dislike? Was this a wrthwhile lab? D yu have any suggestins fr altering it t make it better? What were the hardest parts f it? Did the pints distributin fr the grading seem apprpriate? Did the lab manual cver the material in enugh detail t start yu ff? Did examples r discussins during class help yur understand this lab r wuld mre teaching n the cncepts in this lab help? Make sure that yur cde triggers n errrs r warnings when cmpiling as they will result in a significant lss f pints. Fllw the style guidelines.

4 Submit LinkedList.c, srt.c, and README.txt Grading Pinters This assignment cnsists f 14 pints: 6 pints Prperly implemented dubly-linked list 6 pints Prper srting and printing functinality 1 pint - Prvided a readme file 1 pint Fllws style guidelines (<= 5 errrs in all cde) and has apprpriate cmmenting Yu will lse pints fr the fllwing: NO CREDIT fr sectins where required files dn't cmpile -2: Any cmpilatin warnings. Pinters are cvered very thrughly in the required reading fr this lab, s if yu are having truble refer back t chapter 5 f K&R. Hwever, there is ne cncept abut pinters that is nt directly addressed in the reading: null pinters. A null pinter is a pinter t nthing, which is different than a pinter t zer. These pinters must als be handled as a special case if they are passed t a functin that expects nn-null data pinters. The sectin n functin pinters can be a little verwhelming s t start yu ff here are tw examples f hw t call Print() frm inside main(): Print(listItemPinter, PrintWrd); Dubly-linked lists In cmputer prgrams, much as in real life, keeping a list f things can be necessary. Usually the number f items that will be in this list is knwn ahead f time and s in a cmputer prgram this list culd be kept in a standard C array. There will be ccasins, like when prcessing user input, when the number f items t be stred in a list is nt knwn ahead f time. This is a prblem with C s statically-allcated arrays. The cmmn slutin is t use anther data type called a linked list. Linked lists are exactly what they sund like: a cllectin f bjects that are all linked tgether t frm a single list. As each item is linked t at least ne ther item in the list there is a set rdering t the list: frm a head item at the start t a tail item at the end. Since these items are all cnnected it is easy t access any item frm any ther item by just traversing r walking thrugh the list. Fr this lab yu will be implementing a dubly-linked list, the mre useful sibling f the linked lists. A dubly-linked list is als straightfrward: each item is linked t bth the

5 Selectin srt item befre it and after it. This allws fr traversal f the list frm any element t any ther element by walking alng it, which makes using the list very easy. The items in the list yu are implementing are stred as structs in C because they will be string a few different pieces f data. Specifically it hlds a pinter t the previus ListItem, which will be NULL if it s the head f the list; a pinter t the next ListItem, which will be NULL if it s at the end f the list; and a pinter t any kind f data, NULL if there s n data. The typedef and the name after the } let yu refer t the struct similar t any ther data type, by using the single name ListItem instead f the lnger struct ListItem. The definitin f the ListItem struct in LinkedList.h: typedef struct ListItem { struct ListItem *previusitem; struct ListItem *nextitem; vid *data; } ListItem; Nw that yu understand the structure f a linked list we will intrduce the varius peratins that can be perfrmed upn a list. The standard peratins are creating a new list, adding elements t a list, finding the head f a list, and remving elements frm a list. Creating a new list: A new list is created by just making a single ListItem. As this ListItem is bth the head and tail f the list there is n item befre it r after it in the list. Adding t a list: Nw that yu have a list, hw d yu add mre elements t it? With the arrays that yu are familiar with, yu need t knw tw things: the psitin t insert int and the data that will be inserted. With linked lists it s a little different because there s never a free spt t insert a new item int. What is dne instead is that the psitin f the new list item is relative t an existing item, generally the item befre it in the list. S t insert an item int the list, that item is inserted after an existing item. If the list went A <-> B <-> C and yu want t insert D after B then the list wuld becme A <-> B <-> D <-> C. S that means that the previus item and next item pinters f bth B and C will need t change t accmmdate the new item D. Finding the head: The head f a list is a special item because it has n preceding element (represented by a NULL pinter). Since all the elements in a list are cnnected, finding the head merely requires traversing the list until a list item is fund with n preceding element. A functin that finds the head f the list has ne dd scenari hwever. Remving an element: Remving an element frm a list is the ppsite f adding t it. Fllwing the example abve yu d g frm a list like A <-> B <-> D <-> C t A <-> B <-> C. The pinters f B and C bth need t be mdified t accunt fr the remval f D. Generally the data that was stred within D is als desired after the remval f the item and shuld be returned.

6 Srting is an incredibly imprtant functin in cmputer prgramming. While yu may nt think it is used a lt, it is quite cmmn within a prgram t have the need t srt a series f numbers. Srting is an entire field f study within cmputer science and s there are a huge number f algrithms that d just that. Selectin srt is the ne yu will be fcusing n in this lab. It is very slw n average, but easy t understand and implement. It is called an in-place srting algrithm, because it desn t need t use a temprary array t stre data. Pseud-cde fr selectin srt is prvided belw: fr i = 0 t length(a) 2 d fr j = i + 1 t length(a) - 1 d if A[j] < A[i] d swap A[j] and A[i] end if end fr end fr Selectin srt is best understd by thinking f it as building a srted list n the left by chsing the minimum value frm the riginal unsrted list n the right as the next srted value. The uter fr lp effectively tracks the right-mst element f the srted array filling up the left prtin f the array. This means that fr every iteratin f the uter-lp, the inner-lp can perfrm many element swaps. An example is shwn belw. The left-hand clumn hlds the array at the start f an uter-lp iteratin with the bld items cmprising the already-srted elements. Each swap within the inner-lp is shwn in the right-hand clumn with the bld items having been swapped. The bld items n the left-hand side indicate the nw-srted prtin f the array. Outer lp array Inner-lp swaps Nte: the algrithm yu will be implementing arranges the items in descending rder! mallc(), callc(), and free() This lab als relies n the use f memry allcatin using mallc() (and/r callc()) and free(). These are discussed smewhat in chapter 5 f K&R. As they are standard library functins they are dcumented thrughly nline r in the Linux man-pages. I refer yu t thse resurces t understand them. WARNING: Since Data.a relies n memry allcatin, yu will need t specify a heap size fr yur prject. It shuld be at least 118 bytes. Example Output

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