Tracking Rumors. Suppose that we want to track gossip in a rumor mill

Transcription

1 Tracking Rumors Suppose that we want to track gossip in a rumor mill 1

2 Tracking Rumors Suppose that we want to track gossip in a rumor mill Seiichi 2

3 Tracking Rumors Suppose that we want to track gossip in a rumor mill Seiichi 3

4 Tracking Rumors Suppose that we want to track gossip in a rumor mill Mike Seiichi Lindsey 4

5 Tracking Rumors Suppose that we want to track gossip in a rumor mill Mike Seiichi Amir Lindsey Derrick 5

6 Tracking Rumors Suppose that we want to track gossip in a rumor mill Mike Seiichi Amir Joseph Lindsey Derrick 6

7 Tracking Rumors Simplifying assumption: each person tells at most two others Mike Seiichi Amir Joseph Lindsey Derrick 7

8 Tracking Rumors Simplifying assumption: each person tells at most two others Mike Seiichi Amir Joseph Lindsey Derrick 8

9 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick Is a rumor mill simply a list of people? 9

10 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick Is a rumor mill simply a list of people? No, because there are relationships among people 10

11 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick How about this?: ; A person is ; (make-person image person person)) 11

12 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick How about this?: ; A person is ; (make-person image person person)) No, because some people don t gossip to anyone else or they gossip to an empty rumor mill... 12

13 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick How about this?: ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (define-struct gossip (who next1 next2)) 13

14 Representing Rumor Mills Mike Seiichi Amir Joseph Lindsey Derrick How about this?: ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (define-struct gossip (who next1 next2)) This looks promising... 14

15 Example Rumor Mills ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) empty 15

16 Example Rumor Mills ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (make-gossip empty empty) Joseph 16

17 Example Rumor Mills ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (make-gossip empty (make-gossip empty empty)) Amir Joseph 17

18 Example Rumor Mills ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (make-gossip (make-gossip empty empty) (make-gossip (make-gossip empty (make-gossip empty empty)) (make-gossip empty empty))) Mike Seiichi Amir Joseph Lindsey Derrick 18

19 Example Using Abbreviations (define joseph-mill (make-gossip empty empty)) (define amir-mill (make-gossip empty joseph-mill)) (define derrick-mill (make-gossip empty empty)) (define lindsey-mill (make-gossip amir-mill derrick-mill)) (define mike-mill (make-gossip empty empty)) (define seiichi-mill (make-gossip mike-mill lindsey-mill)) 19

20 Programming with Rumors ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) 20

21 Programming with Rumors ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) 21

22 Programming with Rumors ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (define (func-for-rumor-mill rm) (cond [(empty? rm)...] [(gossip? rm)... (gossip-who rm)... (func-for-rumor-mill (gossip-next1 rm))... (func-for-rumor-mill (gossip-next2 rm))...])) 22

23 Programming with Rumors ; A rumor-mill is either ; - empty ; - (make-gossip image rumor-mill rumor-mill)) (define (func-for-rumor-mill rm) (cond [(empty? rm)...] [(gossip? rm)... (gossip-who rm)... (func-for-rumor-mill (gossip-next1 rm))... (func-for-rumor-mill (gossip-next2 rm))...])) 23

24 Rumor Program Examples Implement the function informed? which takes a person image and a rumor mill and determines whether the person is part of the rumor mill Implement rumor-delay which takes a rumor mill and determines the maximum number of days required for a rumor to reach everyone, assuming that each person waits a day before passing on a rumor Implement add-gossip which takes a rumor mill and two person images one new and one old and adds the new person to the rumor mill, receiving rumors from the old person; the old person must not already have two next persons Implement rumor-chain which takes a person image and a rumor mill and returns a list of person images representing everyone who must pass on the rumor for it to reach the given person; return false if the given person is never informed 24

25 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch 25

26 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch 26

27 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch 27

28 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch 28

29 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch 29

30 More Pipes In the Mid-Term I example, we had all straight pipes in a pipeline Real pipes end in faucets (open or closed) and sometimes branch ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (define-struct straight (kind next)) (define-struct branch (next1 next2)) 30

31 Example Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) false 31

32 Example Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) true 32

33 Example Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (make-straight copper false) 33

34 Example Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (make-straight copper (make-straight lead false)) 34

35 Example Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (make-branch (make-branch (make-straight copper true) false) (make-branch false false)) 35

36 Programming with Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) 36

37 Programming with Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) 37

38 Programming with Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (define (func-for-pipeline pl) (cond [(boolean? pl)...] [(straight? pl)... (straight-kind pl)... (func-for-pipeline (straight-next pl))...] [(branch? pl)... (func-for-pipeline (branch-next1 pl))... (func-for-pipeline (branch-next2 pl))...])) 38

39 Programming with Pipelines ; A pipeline is either ; - bool ; - (make-straight sym pipeline) ; - (make-branch pipeline pipeline) (define (func-for-pipeline pl) (cond [(boolean? pl)...] [(straight? pl)... (straight-kind pl)... (func-for-pipeline (straight-next pl))...] [(branch? pl)... (func-for-pipeline (branch-next1 pl))... (func-for-pipeline (branch-next2 pl))...])) 39

40 Pipeline Examples Implement the function water-running? which takes a pipeline and determines whether any faucets are open Implement the function modernize which takes a pipeline and converts all lead straight pipes to copper Implement the function off which takes a pipeline and turns off all the faucets Implement the function lead-off which takes a pipeline and turns off all the faucets that receive water through a lead pipe Implement the function twice-as-long which takes a pipeline and inserts a copper straight pipe before every existing piece of the pipeline 40