programming's greatest hits of the 60s and 70s

Programming`s Greatest Hits of the

60s and 70s

Michelle Brush Engineering Director, Cerner Corporation

Chapter Leader, Kansas City Girl Develop It Conference Organizer, Midwest.io

Where Are We?

(41.911582, -‐87.634803)

Where Are We?

(41.911582, -‐87.634803)

Latitude: Y value

Where Are We?

(41.911582, -‐87.634803)

Latitude: Y value Longitude: X value

Assuming we have a data store of the locations of all

bars in the world…

https://www.flickr.com/photos/shutterrunner/4334879403/“Today. The Green Door Tavern.” Shutter Runner CC BY 2.0

https://www.flickr.com/photos/shutterrunner/4334879403/

Let’s find a fun place

nearbyto have a beer.

Interview Question:

Write an API to support searching for the nearest bars.

How would you do it?

Right Answer

Google Places API

Sometimes our job is to find ways to not write code.

Let’s rephrase the question.

Interview Question:

Write an API to support searching for the nearest bars

from scratch.

How would you do it?

Binary Search2 4 7 9 11 13 34 37 92 1050 1 2 3 4 5 6 7 8 9

?

?

?Found It!

Everyone used to know binary search.

They just didn’t know what it was called.

(cc) http://www.recyclethis.co.uk(and picked inefficient pivot points)

SOME SORTING REQUIRED.

INSERT SORT ALGORITHM NOW.

Sort by X, then Y!

Well, that breaks.

Which is closer?

United Lily Growers

in Smith River California

~1800 miles

The Green Door Tavern

not that far in Chicago

1.26 miles

or

X gets preferential treatment over Y.

It doesn’t deserve it.

How about brute force?

1. Iterate over every bar. 2. Calculate the distance. 3. Sort by the distance.

1630 bars in Chicago alone.

Is there a right answer?

Was I just a mean interviewer?

Some people got it right.

Physics Majors

In particular…

Physics majors that care about particle collisions.

Divide & Conquer the Space

Rules

Quadrants are not always equal in space.

They can be equal in capacity.

Capacity = Number of Objects

Center Point

(X, Y)

Or Bounding Box

( X1, Y1 )

( X2, Y2 )

Create a Tree of Nested Quadrants

Follow the Rectangles Down

1974

Jon L. Bentley & Raphael Finkel

Quad-Trees

1974

Jon L. Bentley (includes buggy implementation of binary search)

Quad-tree is a very good answer.

It can be generalized to more dimensions.

Octrees

WhiteTimberwolf 2010, Schematic drawing of an octree, a data structure of computer science.

https://commons.wikimedia.org/wiki/User:WhiteTimberwolf

https://en.wikipedia.org/wiki/Octree

Binary Search2 4 7 9 11 13 34 37 92 1050 1 2 3 4 5 6 7 8 9

?

?

?Found It!

SOME SORTING REQUIRED.

INSERT SORT ALGORITHM NOW.

I have 2 values. I need 1.

Bit Concatenation

(x, y)

(x3x2x1x0, y3y2y1y0)

x3x2x1x0 y3y2y1y0

(9, 3)

(1001, 0011)

10010011

Bit Interleaving

(x, y)

(x3x2x1x0, y3y2y1y0)

x3y3x2y2x1y1x0y0

(9, 3)

(1001, 0011)

10000111

1966

G.M. Morton

Z Order

3 (0,3) (1,3) (2,3) (3,3)

2 (0,2) (1,2) (2,2) (3,2)

1 (0,1) (1,1) (2,1) (3,1)

0 (0,0) (1,0) (2,0) (3,0)

0 1 2 3

3 1010 10

1011 11

1110 14

1111 15

2 1000 8

1001 9

1100 12

1101 13

1 0010 2

0011 3

0110 6

0111 7

0 0000 0

0001 1

0100 4

0101 5

0 1 2 3

3 1010 10

1011 11

1110 14

1111 15

2 1000 8

1001 9

1100 12

1101 13

1 0010 2

0011 3

0110 6

0111 7

0 0000 0

0001 1

0100 4

0101 5

0 1 2 3

Newly created number determines order.

3 1010 10

1011 11

1110 14

1111 15

2 1000 8

1001 9

1100 12

1101 13

1 0010 2

0011 3

0110 6

0111 7

0 0000 0

0001 1

0100 4

0101 5

0 1 2 3


start

3 1010 10

1011 11

1110 14

1111 15

2 1000 8

1001 9

1100 12

1101 13

1 0010 2

0011 3

0110 6

0111 7

0 0000 0

0001 1

0100 4

0101 5

0 1 2 3


start

finish

3101010

101111

111014

111115

210008

10019

110012

110113

1 00102

00113

01106

01117

0 00000

00011

01004

01015

0 1 2 3

(0,0)

(1,1)

space-filling curve

Bit-interleaving can be extended to

multiple dimensions.

from space to graphs…

lost in suburbia

Blue Spruce Dr.

Arborwood Ct.

Elmwood St.

Blue Fir Ln.

Go right.

Go right.

19th CenturyCharles Pierre Trémaux

depth-first search

BREADTH-FIRST SEARCH

BREADTH-FIRST SEARCH1950s

A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

Open List

A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

Open List

A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

sum of all costs to get here

Open List Closed List

A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

sum of all costs to get here


A 0

A


A 0

A

B2

C3

D4


A 0

A

B2

C3

D4

B 2

C 3

D 4


B 2

C 3

D 4

A 0

A

B2

C3

2

D4

E

4

My Example Graph


C 3

D 4

E 6

A 0

B 2

A

B2

C3

2

D4

E

4

My Example Graph


C 3

D 4

E 6

A 0

B 2

A

B2

C3

2

D4 2

E1

4

My Example Graph


D 4

E 4

A 0

B 2

C 3

A

B2

C3

2

D4 2

E1

4

My Example Graph


E 4 A 0

B 2

C 3D 4A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

1956

Edsger W. Djikstra

Djikstra’s Algorithm

Hamilton Richards - manuscripts of Edsger W. Dijkstra, University Texas at Austin

http://www.cs.utexas.edu/users/EWD/

1968

Peter Hart, Nils Nilsson, & Bertram Raphael

A*A


A

B2

C3

2

D4 2

E

4

1

4

My Example Graph

sum cost to get here plus distance to goal

0

2

2

13


A 3

A

B2

C3

D4

My Example Graph

2

2

13


B 4

C 4

D 6

A 3

A

B2

C3

D4

My Example Graph

2

2

13


A 3

A

B2

C3

2

D4

E

4

My Example Graph

0

2

2

13

B 4

C 4

D 6


A 3

B 4

A

B2

C3

2

D4

E

4

My Example Graph

0

2

2

13

C 4

D 6

E 6


A

B2

C3

2

D4 2

E1

4

My Example Graph

0

2

2

13

A 3

B 4

C 4

D 6

E 6


A

B2

C3

2

D4 2

E1

4

My Example Graph

0

2

2

13

A 3

B 4

C 4

E 4

D 6


A

B2

C3

2

D4 2

E1

4

My Example Graph

0

2

2

13

A 3

B 4

C 4

E 4

D 6

We didn’t have to close D.

Breadth-first Search



A*

The power of heuristics.



A*

Are all edge weights equal?

What’s your most expensive operation?

Do you have insights about your target?

Breadth-First

Djikstra

A*

yes

no

visitshe

uristic

s

?

?

?

breadth-first search f(x) = c

djikstra’s algorithm f(x) = g(x) + c

a* f(x) = g(x) + h(x) + c

The others were specializations.

and we can do more than search with graphs…

1974

Charles L. Forgy

Rete

Premise 1

Premise 2

Premise 3

Conclusion

Rules

Premise 1

Premise 2

Premise 3

Take Action

Rules

(Premise 1, Premise 2, Premise 3)

(Action)

=>


(Action)

=>Left Hand Side


(Action)

=>Left Hand Side

Right Hand Side

A

B

C

D

ERules are a

directed acyclic graph.

like a trie

C

I OH

I DT

C EY

A K

G E

O N

Root Node

Root Node

Type Nodes

Root Node

Selection Nodes

Type Nodes

Root Node

Negation Nodes

Selection Nodes

Type Nodes

Root Node

Join Nodes

Negation Nodes

Selection Nodes

Type Nodes

Root Node

Terminal Nodes

Join Nodes

Negation Nodes

Selection Nodes

Type Nodes

Root Node

Alpha Memory

Terminal Nodes

Join Nodes

Negation Nodes

Selection Nodes

Type Nodes

Root Node

Beta Memory

Alpha Memory

Terminal Nodes

Join Nodes

Negation Nodes

Selection Nodes

Type Nodes

recommend-diet-changes

Hypertension (severity == moderate)

Demographics (age > 60)

prescribe-bp-meds

Hypertension

HypertensionDemographics

Hypertension (severity == moderate)

Ryan Brush “Retaking Rules for Developers”

Hypertension

Demographics Hypertension (severity == moderate)

Demographics (age > 60)

recommend-diet-changes

prescribe-bp-meds

Ryan Brush “Retaking Rules for Developers”

Sometimes our job is to find ways to not write code.

Let’s not build an expert system!

(-‐>clara)

Let’s not build an expert system!

(-‐>clara)

+

=

Triskel99 - Own work AMC Pacer, photographed during August 2009.

https://commons.wikimedia.org/w/index.php?title=User:Triskel99&action=edit&redlink=1

Efficacy

Cost

Convenience

import java.util.Comparator;

public class ChoiceComparator implements Comparator<Choice> {

@Override public int compare(Choice o1, Choice o2) { if( o2.getEfficacy() == o1.getEfficacy) { if( o2.getCost() == o1.getCost) { return o2.getConvenience() -‐ o1.getConvenience(); } return o2.getCost() -‐ o1.getCost(); } return o2.getEfficacy() -‐ o2.getEfficacy(); } }

public class EfficacyComparator implements Comparator<Choice>

public class CostComparator implements Comparator<Choice>

public class ConvenienceComparator implements Comparator<Choice>

1.SORT 2.TAKE 10 3.GOTO 1

1974

Jon L. Bentley & Raphael Finkel

Quad-Trees

1966

G.M. Morton

Z Order

for(int i = 0; i < count1; ++i) { for(int j = 0; j < count2; ++j) { for(int k = 0; k < count3; ++k) { for(int l = 0; l < count4; ++l) { for(int m = 0; m < count5; ++m) { for(int n = 0; n < count6; ++n) { for(int o = 0; o < count7; ++o) { for(int p = 0; p < count8; ++p) { for(int q = 0; q < count9; ++q) { for(int r = 0; r < count10; ++r) { for(int s = 0; s < count 11 for(int t = 0; t < count for(int u = 0; for(int v = 0 for(int w for(i fo

for-nado?

You are using the wrong algorithm.

Crack open an algorithms book.

Do a Depth-First Search of Wikipedia

Your solution is out there.

BLOOM FILTER

trie

Gale Shapley

A*

R-Tree

TREAP

Dijkstra’s

Floyd Warshall

D* Hu

ffm

anID

3

CARTRet

e

And to be honest…

It is probably from the 60s or 70s.

1979Engineering Director, Cerner Corporation Chapter Leader, Kansas City Girl Develop It Conference Organizer, Midwest.io

@michellebrush

Michelle Brush

programming's greatest hits of the 60s and 70s

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