dig 3134 – lecture 19: intellectual overload: flood filling and recursion and json

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DIG 3134 – Lecture 19:

Intellectual Overload:Flood Filling

andRECURSION

and JSON

Michael MoshellUniversity of Central Florida

Internet Software Design

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SnakeWall: let's play the game

• Well, it's a bit of a• LAME GAME, but-I expect we can -improve on it

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Goal: Build a bridge to other side

• Players take turns• enter x, y, (b or g)OR• Check the radio button + color.

PLAY THE GAME(wall/wall04.php)

Develop Ideas About game play.

•X• Y

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Implementing a Rule

WHAT IF we had a rule:

Each new tile (black or gold) must be NEXT TO a tile that's already black or gold?

Define a function like this:

function goodplay($color,$x,$y)

That returns TRUE (or 1) if it is legal to playthe color $color at location ($x,$y)

And it returns FALSE (or 0) if not.

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Can black draw at (4,6)?

Exercise:Talk to people around you.

Talk to the peopleIn front of, to the Left of, to the right of,Behind you.

Can you think up theAlgorithm, in English?

•X• Y

?

6666

Can black draw at (4,6)?

Answer #1:No, becauseIt's Gold's turn!

(But that's a trickAnswer. A moreLegitimate answerIs ….)

•X• Y

?

7777

Can black draw at (4,6)?

$b=BLACK;If (($Grid[$x-1][[$y]==$b)||($Grid[$x+1][$y]==$b)||($Grid[$x][$y-1]==$b)||($Grid[$x][$y+1]==$b) ) return 1; else return 0;

•X• Y

?

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An exam practice question

$b=BLACK;If (($Grid[$x-1][[$y]==$b)||($Grid[$x+1][$y]==$b)||($Grid[$x][$y-1]==$b)||($Grid[$x][$y+1]==$b) ) return 1; else return 0;

How would youModify this rule If diagonal movesWere allowed?

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Now for the ultimate challenge

Advanced players mightNot require contiguous moves.

Can we find a way toAUTOMATICALLYDetect a winner?

We need software that canDetect the existence of a complete path, however crooked and forked!

10101010101010

Now for the ultimate challenge:

Like this one,Where Black has justCompleted a path.

If we could 'flood fill'The path to test it…

1111111111111111

Flood-filling to find a win-path

Like this one,Where Black has justCompleted a path.

If we could 'flood fill'The path to test it…

Then we would just put a test in the floodfill function, to see if we ever try to fill a cell where $y>$Tablewidth.

If so, declare a winner!

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A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

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A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5)

14141414141414

A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5) 5*factorial(4)

15151515151515

A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5) 5*factorial(4) 4*factorial(3)

3*factorial(2) 2*factorial(1)

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A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5) 5*factorial(4) 4*factorial(3)

3*factorial(2) 2*factorial(1)which is 2*1=2

17171717171717

A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5) 5*factorial(4) 4*factorial(3)

3*factorial(2) 2*factorial(1)which is 2*1=2

yielding 3*2=6 yielding 4*3=12

18181818181818

A Diversion: RECURSION!

A recursive function is one that calls a copy of itself!

consider this famous example:

function factorial($n){

if ($n<=1) return 1;else return $n*factorial($n-1);

}print factorial(5);

factorial(5) 5*factorial(4) 4*factorial(3)

3*factorial(2) 2*factorial(1)which is 2*1=2

yielding 3*2=6 yielding 4*3=12 yielding 5*12=60returns 60

191919191919191919

Flood-filling

function floodfill($oldcol,$newcol,$x,$y) { global $Grid;

$thiscolor=$Grid[$x][$y];if (($x<0)||($y<0)||($thiscolor==BLUE))

return; if ($thiscolor==$oldcol) // time to go to work!{ $Grid[$x][$y]=$newcol;

floodfill($oldcol,$newcol,$x-1,$y);floodfill($oldcol,$newcol,$x+1,$y);floodfill($oldcol,$newcol,$x,$y-1);floodfill($oldcol,$newcol,$x,$y+1);

} } #floodfill

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Recursion

A function which calls itself is called a recursive function.

This is NOT the same as repetition (like a FOR loop).It is much more powerful (and dangerous!)

Powerful: it can figure out many tree shaped problems,like playing chess (or flood filling)

Dangerous: if you don't terminate it properly, it willhang up and run forever. "down the rabbit hole"

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Recursion

Why is this so powerful?Consider an expression like

$x=($z + 4*$y)/(*$z-3*$y);

It seems complex to analyze it. But most computer languages

use a recursive system, like this:evaluator($expression){

If $expression is of form $n x $b where xis an operator (+ - * /) then compute it

else break it into parts $a and $b, andapply evaluator () to both parts.

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JSON – wazzat?

If you need to store complex data in a text file(for instance, a string indexed array)

You COULD role your own code (I did, before JSON)and debug it, and maintain it, etc...

OR you could meet ...

23232323232323232323

JSON – wazzat?

If you need to store complex data in a text file(for instance, a string indexed array)

You COULD role your own code (I did, before JSON)and debug it, and maintain it, etc...

OR you could meet ...

24242424242424242424

JSON – wazzat?

If you need to store complex data in a text file(for instance, a string indexed array)

You COULD role your own code (I did, before JSON)and debug it, and maintain it, etc...

OR you could meet ...

(oh ... sorry, wrong JASON)

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JSON – JavaScript Object Notation

Example from wikipedia:{"firstName": "John", "lastName": "Smith", "isAlive": true, "age": 25, "height_cm": 167.64, "address": {

"streetAddress": "21 2nd Street", "city": "New York", "state": "NY", "postalCode": "10021-3100"

}

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JSON – JavaScript Object Notation

{ "firstName": "John", "lastName": "Smith", "isAlive": true, "age": 25, "height_cm": 167.64, "address": { "streetAddress": "21 2nd Street", "city": "New York", "state": "NY", "postalCode": "10021-3100" }}

Self-documenting data – similar to XMLbut simplerand more

compact

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JSON for Problem Solving

I was building a complex application for my grad student, Dave Moran

I needed to store and recover a big messy record called a Picture Dictionary

JSON built into PHP was the perfect tool.

<<Demonstration of Moran-Vision Software>>

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JSON for Problem Solving

I was building a complex application for my grad student, Dave Moran

I needed to store and recover a big messy record called a Picture Dictionary

JSON built into PHP was the perfect tool.

<<Demonstration of Moran-Vision Software>>

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JSON for Problem Solving

The actual JSON file looks like a MESS:

{"File Name":{"wordlist":[["tag 2",0,0],["tag 3",0,0],["tag 4",0,0],["tag 5",0,0],["tag 6",0,0],["tag 7",0,0],["tag 8",0,0],["tag 9",0,0],["tag 10",0,0],["tag 11",0,0]],"zone":"Page"},"245":{"pictureid":245,"filename":"245","wordlist":[["hellafaya",0,0],["i",0,0],["am",0,0],["raphael",0,0],["iamraphael",0,0],["pattern",0,0],["of",0,0],["behavior",0,0],["patternofbehavior",0,0],["teenage",0,0],["mutant",0,0],["ninja",0,0],["turtles",0,0],["teenagemutantninjaturtles",0,0],["running",0,0],["with",0,0],["scissors",0,0],["runningwithscissors",0,0],["wired",0,0],["fabric",0,0],["softener",0,0],["fabricsoftener",0,0],["black",0,0],["and",0,0],["white",0,0],["blackandwhite",0,0],["from",0,0],["where",0,0],["i",0,0],["stand",0,0],["fromwhereistand",0,0],["scissors",

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JSON for Problem Solving

The data, viewed by print_r, is nicer (if you VIEW SOURCE)

[245] => stdClass Object (

[pictureid] => 245[filename] => 245 [wordlist] => Array ( [0] => Array (

[0] => hellafaya [1] => 0 [2] => 0 )

[1] => Array ( [0] => i [1] => 0 .. etc etc ...

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JSON for Trickery

Remember XML? Its loader creates a complex OBJECT.But what if we wanted an ARRAY?

json_encode and decode is a sneaky way to performa quick switcheroo:

$xml = simplexml_load_file('xml_file.xml');    $json_string = json_encode($xml);    $result_array = json_decode($json_string, TRUE);

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JSON for Trickery

$xml = simplexml_load_file('xml_file.xml');    $json_string = json_encode($xml);    $result_array = json_decode($json_string, TRUE);

These are built-in PHP functions. You can simply file-writethe encoded JSON string; etc.

Take-away: JSON provides convenient storage for complexobjects (like arrays-of-arrays).

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That's it for today.

Next (and last) Lecture:

Strategies for Success asa Programmer

anda Human Being

AND – a raffle! Win good junk.

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