COMP26120: Algorithms and Imperative Programming

Transcription

1 COMP26120 ecure C3 1/48 COMP26120: Algorihms and Imperaive Programming ecure C3: C - Recursive Daa Srucures Pee Jinks School of Compuer Science, Universiy of Mancheser Auumn 2011

2 COMP26120 ecure C3 2/48 Review Inpu/Oupu: sdio, sreams/fie*, (f)prinf, fges, (s)scanf Arrays: 1-D + muli-d, Srings Poiners: &, *, Reference, Array + Funcion Parameers Daa srucures: Sruc, Union, Enum Simpler ype-names: Typedef Poiners again: Malloc C doesn have Garbage Collecion: Free, Valgrind

3 COMP26120 ecure C3 3/48 ecure Ouline inked iss (ab 8) ab 8.1: Inser a sar of lis ab 8.2: Inser a end of lis ab 8.3: Inser in order ab 8.6: Poiner o Poiner Make & Makefiles Implemening Make Trees (ab 9)

4 COMP26120 ecure C3 inked iss (ab 8) 5/48 Wha is a inked is? e.g. a lis of 3 iems, wih each iem conaining a sruc person {char *name; in age;}; s a r name1 age1 name2 age2 name3 age3 N U The firs iem in a lis is he head and he res of he lis is he ail. (so a lis of jus 1 iem has an empy ail)

5 OMP26120 ecure C3 inked iss (ab 8) 6/48 Implemenaion Moodle heme: Informaion Represenaion Moodle: inked iss Q: How do we need o change sruc person {char *name; in age;};? Q: How do we declare and iniialise he lis o be empy?

6 COMP26120 ecure C3 inked iss (ab 8) 8/48 e.g. pu (name4, age4) a sar of lis n e w s name4 a r age4 o l d s a r name1 age1 name2 age2 name3 age3 N U

7 COMP26120 ecure C3 inked iss (ab 8) 9/48 Quesion: C code? Creae and iniialse new person, and inser a sar of lis, seing new sar

8 COMP26120 ecure C3 inked iss (ab 8) 11/48 e.g. pu (name4, age4) a end of lis name4 age4 N U s a name1 name2 name3 r age1 age2 age3

9 OMP26120 ecure C3 inked iss (ab 8) 12/48 Implemenaion Q: If he curren lis is empy? Q: If i isn empy, we need o find he las iem in he lis and hen? Q: How o find he las iem in he lis?

10 COMP26120 ecure C3 inked iss (ab 8) 14/48 e.g. pu (name4, age4) in lis suppose name1 < name4 < name2 < name3 name4 age4 s a r name1 age1 name2 age2 name3 age3 N U

11 COMP26120 ecure C3 inked iss (ab 8) 16/48 Implemenaion Trickier, because each es becomes wo: eiher here isn anoher iem on he lis or here is, and he new iem should precede i if lis is empy or new person < firs lis iem inser new person a sar of lis oherwise loop down he lis unil new person should immediaely follow lis iem eiher because lis iem < new person < (lis iem >nex) or because lis iem is he end of he lis and inser here

12 COMP26120 ecure C3 inked iss (ab 8) 19/48 ** In C, a poiner can poin o anyhing, even anoher poiner e.g. in i; in *p = &i; in **p2p = &p; **p= 1; If we use sruc person** p2p; we can combine similar ess (in he iniial if and in he loop) and reduce he amoun of code.

13 COMP26120 ecure C3 inked iss (ab 8) 20/48 p2p = &sar; sruc person** p2p; sruc person* sar; p 2 p s a r name1 age1 name2 age2 name3 age3 N U

14 COMP26120 ecure C3 inked iss (ab 8) 21/48 p2p = &sar; (*p2p) >name is name1 p 2 p s a r name1 age1 name2 age2 name3 age3 N U *p2p or (*p2p) is he value of sar (*p2p)->name is he value of sar->name i.e. name1

15 COMP26120 ecure C3 inked iss (ab 8) 22/48 Sep along lis p 2 p s a r name1 age1 name2 age2 name3 age3 N U *p2p or (*p2p) is he value of sar (*p2p)->nex is he value of sar->nex &((*p2p)->nex) is a poiner o sar->nex

16 COMP26120 ecure C3 inked iss (ab 8) 23/48 p2p= &((*p2p) >nex); (*p2p) >name is name2 p 2 p s a r name1 age1 name2 age2 name3 age3 N U

17 COMP26120 ecure C3 inked iss (ab 8) 24/48 p2p= &((*p2p) >nex); (*p2p) >name is name3 p 2 p s a r name1 age1 name2 age2 name3 age3 N U

18 COMP26120 ecure C3 inked iss (ab 8) 25/48 p2p= &((*p2p) >nex); (*p2p)==nu p 2 p s a r name1 age1 name2 age2 name3 age3 N U

19 OMP26120 ecure C3 inked iss (ab 8) 26/48 Wha if he lis was empy? p 2 p s a r N U (*p2p)==nu If we use sruc person** p2p; we can combine similar ess (in he iniial if and in he loop) and reduce he amoun of code. In boh cases, we modify he sruc person * ha p2p poins a.

20 COMP26120 ecure C3 Make & Makefiles 28/48 Make Simple conrol of compilaion: e.g. make fred Projec managemen: (i.e. many files) If I edi a file, wha is he minimum I need o do o rebuild everyhing? Compares file ime-samps o see wha needs re-building Conrolled by rules in a makefile

21 COMP26120 ecure C3 Make & Makefiles 29/48 Makefile Buil-in Rules: make fred auomaically from fred.c by e.g. gcc -Wall -g -sd=c99 -lm fred.c -o fred Explici rules in makefile: oupu file(s): inpu file(s) command(s) o make oupu(s) from inpu(s) also phony rules oupu(s) ha aren files.phony: 1 1: par1 par1

22 COMP26120 ecure C3 Implemening Make 32/48 A very simple Make all rules explici: 1 arge, 1 command, 2 inpus e.g. makefile: a_z: a z sor a z >a_z a: b c merge b c >a z: x y combine x y >z

23 COMP26120 ecure C3 Implemening Make 35/48 Inernal represenaion a_z: a z sor a z >a_z a: b c merge b c >a z: x y combine x y >z Roo of ree = a z node b c x y \ / \ / merge combine \ / a z \ / sor a_z A ree

24 OMP26120 ecure C3 Implemening Make 37/48 Building he ree Simplify srucure: b c x y \ / \ / a,merge z,combine \ / a_z,sor Implemen ree using srucs, poiners ec. \ / a,merge Wrie he sruc in C:

25 OMP26120 ecure C3 Implemening Make 39/48 make a b c x y \ / \ / a,merge z,combine \ / a_z,sor find a in ree, check files b and c exis, check a is up-o-dae (compare file ime-samps) if no, run command merge

26 COMP26120 ecure C3 Implemening Make 41/48 make a z b c x y \ / \ / a,merge z,combine \ / a_z,sor find a z in ree check file a up-o-dae if no, make a check file z up-o-dae if no, make z run command sor make calls iself: recursion

27 COMP26120 ecure C3 Implemening Make 42/48 Searching Easy o wrie a loop o search a lis: sruc person* emp= lis; while (emp!=nu && srcmp(emp->name, newname)!=0) emp= emp->nex; Bu how do we wrie a loop o search down a ree? how do we follow boh branches?

28 Searching a ree (los more nex semeser) Saring a he roo of he ree, Does his node mach? If no, is here a mach on he lef? If no, is here a mach on he righ? search (hisnode, filename): // reurn poiner o node maching filename or NU if hisnode is NU, reurn i if hisnode->filename maches, reurn hisnode if search (hisnode->lef, filename) isn NU, reurn i reurn search (hisnode->righ, filename) This uses recursion (again) This search is roo-firs, lef-o-righ How do we search righ-o-lef? How do we search roo-las? COMP26120 ecure C3 Implemening Make 43/48

29 OMP26120 ecure C3 Implemening Make 44/48 Building he ree from he makefile a z: a z sor a z >a z 1) build nodes for: a z + sor, a, z 2) link hem ogeher 3) ree a z a: b c merge b c >a 4) search ree for a, add merge 5) build nodes for b, c 6) link hem ogeher...

30 COMP26120 ecure C3 Implemening Make 45/48 Recursive Daa-Types (RDT) A lis is empy or a node (head) + he res of he lis (ail), which is iself a lis A binary (2-way) ree is empy or a node (roo) + (up o) wo subrees (children) A ernary (3-way) ree is empy or a node (roo) + (up o) hree subrees (children)...

31 COMP26120 ecure C3 Implemening Make 47/48 Nex ecure: Complexiy Joshua Knowles Ge hold of Goodrich and Tamassia: Algorihm Design main library, Joule library, School, Blackwells. Reading: pp Asympoic Noaion pp Mahs review Bring a calculaor

32 COMP26120 ecure C3 Implemening Make 48/48 ecure Review inked iss (ab 8) ab 8.1: Inser a sar of lis ab 8.2: Inser a end of lis ab 8.3: Inser in order ab 8.6: Poiner o Poiner Make & Makefiles Implemening Make Trees (ab 9)