dig 3134 – lecture 19: intellectual overload: flood filling and recursion and json
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Internet Software Design. DIG 3134 – Lecture 19: Intellectual Overload: Flood Filling and RECURSION and JSON Michael Moshell University of Central Florida. SnakeWall: let's play the game. Well, it's a bit of a LAME GAME, but I expect we can improve on it. - PowerPoint PPT PresentationTRANSCRIPT
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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
?
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Can black draw at (4,6)?
Answer #1:No, becauseIt's Gold's turn!
(But that's a trickAnswer. A moreLegitimate answerIs ….)
•X• Y
?
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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!
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Now for the ultimate challenge:
Like this one,Where Black has justCompleted a path.
If we could 'flood fill'The path to test it…
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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)
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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)
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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)
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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
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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
yielding 3*2=6 yielding 4*3=12 yielding 5*12=60returns 60
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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 ...
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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 ...
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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