[RESOLVED] unset the previous array in a recusive function

jrough


function count_chairs($arr)
  {
  // how many elements in array
  $i = count($arr);
echo $i;

  // Creat an index to positions 0, 2, 4, ... $i
  $index = range(1, $i, 2);


  // Return the data at positions 0, 1, 2, ...
  $out = array();
  foreach($index as $key)
	{
	if(array_key_exists($key, $arr))

  {


 $out[] = $arr[$key];
  }
}

  return($out);
  }



$arychairs= range(1,100);

while(count( $arychairs ) > 1 )
  {
  $arychairs = count_chairs($arychairs);

  echo "<pre>";
    print_r($arychairs);
  echo "</pre>";
  }

There is something not quite right with this algorithm I'm having trouble figuring what.
According to the current function the last chair is 64 but that is not the right surviving chair.

this is the output:
Array
(
[0] => 2
[1] => 4
[2] => 6
[3] => 8
[4] => 10
[5] => 12
[6] => 14
[7] => 16
[8] => 18
[9] => 20
[10] => 22
[11] => 24
[12] => 26
[13] => 28
[14] => 30
[15] => 32
[16] => 34
[17] => 36
[18] => 38
[19] => 40
[20] => 42
[21] => 44
[22] => 46
[23] => 48
[24] => 50
[25] => 52
[26] => 54
[27] => 56
[28] => 58
[29] => 60
[30] => 62
[31] => 64
[32] => 66
[33] => 68
[34] => 70
[35] => 72
[36] => 74
[37] => 76
[38] => 78
[39] => 80
[40] => 82
[41] => 84
[42] => 86
[43] => 88
[44] => 90
[45] => 92
[46] => 94
[47] => 96
[48] => 98
[49] => 100
)

Array
(
[0] => 4
[1] => 8
[2] => 12
[3] => 16
[4] => 20
[5] => 24
[6] => 28
[7] => 32
[8] => 36
[9] => 40
[10] => 44
[11] => 48
[12] => 52
[13] => 56
[14] => 60
[15] => 64
[16] => 68
[17] => 72
[18] => 76
[19] => 80
[20] => 84
[21] => 88
[22] => 92
[23] => 96
[24] => 100
)

Array
(
[0] => 8
[1] => 16
[2] => 24
[3] => 32
[4] => 40
[5] => 48
[6] => 56
[7] => 64
[8] => 72
[9] => 80
[10] => 88
[11] => 96
)

Array
(
[0] => 16
[1] => 32
[2] => 48
[3] => 64
[4] => 80
[5] => 96
)

Array
(
[0] => 32
[1] => 64
[2] => 96
)

Array
(
[0] => 64
)

The first returned array is right, it removes 1,3,5,...99 and leaves chairs 2,4,6...100.
The second array is wrong. It should leave chairs 6,14,22,38,46,54,62,70,78,86 &94 instead of 4,8,12,16,20,24...100.

Maybe it is just not removing what was already removed? HOw do I unset the first set before starting on the second set in the foreach? I think that will solve it.
The problem again:
You are in a room with a circle of 100 chairs. The chairs are numbered sequentially from 1 to 100, the person in chair #1 will be asked to leave. The person in chair #2 will be skipped, and the person in chair #3 will be asked to leave. This pattern of skipping one person and asking the next to leave will keep going around the circle until there is one person left.
thanks again.

jrough

P.S another thing that might be wrong is it needs to start on the 1st index if the last index on the previous pass was removed otherwise it has to skip one. It is pretty complicated.

leatherback

I think the problem lays more in that you want to do something recursively, which is not recursive. The orginal problem you posted was: I need a recursive function that removes every second item from an array, starting with the first element. If you do that recursively, then you end up removing both head and tail values. Maybe you should explain better what you want to end up with? Because the thing you ask for now is completely different:

The first run: Remove every second item, starting with item one
The second run: You want to return values that are at positions:

2 - 6- 10 -15 - 22 - 26 (Giving intervals of 4 - 4 - 5 - 7 - 4 ) in the array poroduced after the first run. There does not seem to be any logic in there..

leatherback

OK, the final paragraph does ectually explain better what you are trying to do. No server here to test the script, but I think this is what you are trying to do:


function dropthem($var, $remove)
  {
  $new = array();
  foreach($var as $val)
    {
    if($remove)
      {
      $remove = false;
      }
    else
      {
      $remove = true;
      $new[] = $val;
      echo $val;
      }
    }
  dropthem($new, $remove);
  }

//fill array
$arychairs= range(1,100);

drop_them($arychairs);

jrough

I guess I assumed it was recursive when it wasn't. I will start over with the one before it become recursive. The numbers I got was by doing it manually. Counting out 100 and removing every other one. I guess I have to check the tail if there is a value then skip the head. thanks,

jrough

Okay, thanks I am going to test your script now but in my own way I was trying it procedurally. The below results seem weird. Why is there an empty value in the 3rd pass?

<?php

function count_chairs_even($arr) {
	// how many elements in array
  		$i = count($arr);

  // Creat an index to positions 0, 2, 4, ... $i
  		$index = range(1, $i, 2);

  // Return the data at positions 0, 1, 2, ...
  	$out = array();
  	foreach($index as $key)
    	{
 		$out[] = $arr[$key];
    	}	

  return $out;	
 }

function count_chairs_odd($arr) {
	// how many elements in array
  		$i = count($arr);

  // Creat an index to positions 0, 2, 4, ... $i
  		$index = range(1, $i, 2);

  // Return the data at positions 0, 1, 2, ...
  	$out = array();
  	foreach($index as $key)
    	{
 		$out[] = $arr[$key];
    	}	

  return $out;	
 }
//fill array
$arychairs= range(1,100);
$pass1= count_chairs_even($arychairs);
$pass2= count_chairs_even($pass1);
$pass3= count_chairs_even($pass2);

echo "<pre>" . "Pass1" ." ";
  print_r($pass1);
echo "</pre>";

echo "<pre>". "Pass2" . " ";
  print_r($pass2);
echo "</pre>";

echo "<pre>". "Pass3" . " ";
  print_r($pass3);
echo "</pre>";


?>

Pass1 Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
    [4] => 10
    [5] => 12
    [6] => 14
    [7] => 16
    [8] => 18
    [9] => 20
    [10] => 22
    [11] => 24
    [12] => 26
    [13] => 28
    [14] => 30
    [15] => 32
    [16] => 34
    [17] => 36
    [18] => 38
    [19] => 40
    [20] => 42
    [21] => 44
    [22] => 46
    [23] => 48
    [24] => 50
    [25] => 52
    [26] => 54
    [27] => 56
    [28] => 58
    [29] => 60
    [30] => 62
    [31] => 64
    [32] => 66
    [33] => 68
    [34] => 70
    [35] => 72
    [36] => 74
    [37] => 76
    [38] => 78
    [39] => 80
    [40] => 82
    [41] => 84
    [42] => 86
    [43] => 88
    [44] => 90
    [45] => 92
    [46] => 94
    [47] => 96
    [48] => 98
    [49] => 100
)
Pass2 Array
(
    [0] => 4
    [1] => 8
    [2] => 12
    [3] => 16
    [4] => 20
    [5] => 24
    [6] => 28
    [7] => 32
    [8] => 36
    [9] => 40
    [10] => 44
    [11] => 48
    [12] => 52
    [13] => 56
    [14] => 60
    [15] => 64
    [16] => 68
    [17] => 72
    [18] => 76
    [19] => 80
    [20] => 84
    [21] => 88
    [22] => 92
    [23] => 96
    [24] => 100
)
Pass3 Array
(
    [0] => 8
    [1] => 16
    [2] => 24
    [3] => 32
    [4] => 40
    [5] => 48
    [6] => 56
    [7] => 64
    [8] => 72
    [9] => 80
    [10] => 88
    [11] => 96
    [12] => 
)

jrough

I tested it but couldn't get the internal function to go there is a syntax error.

There was one type-o drop-them instead of dropthem. Other than that I couldn't figure it out. I thought maybe it didn't know the false/ true so I added it explicitly but it still hangs on the internal recursive function?

<?php

function dropthem($var,$remove)
{
  $new = array();
  foreach($var as $val)
    {
    if($remove="false" || $remove="")
      {

  $remove = false;
  }
else
  {
  $remove = true;
  $new[] = $val;
  echo $val;
  }
}
 dropthem($new, $remove="true");
}

//fill array
$arychairs = range(1,100);

dropthem($arychairs);
?>

jrough

CAn the last chair be 36?
It would be good if I could check my value with your function. I don't know if the logic is right on this but I changed the index when the chairs were an odd number. I'm not exactly sure from
$index = range(1, $i, 2);
to
$index = range(0, $i, 2);

<?php

function count_chairs_even($arr) {
	// how many elements in array
  		$i = count($arr);

  // Creat an index to positions 0, 2, 4, ... $i
  		$index = range(1, $i, 2);

  // Return the data at positions 0, 1, 2, ...
  	$out = array();
  	foreach($index as $key)
    	{
 		$out[] = $arr[$key];
    	}	

  return $out;	
 }

function count_chairs_odd($arr) {
	// how many elements in array
  		$i = count($arr);

  // Creat an index to positions 0, 2, 4, ... $i
  		$index = range(0, $i, 2);

  // Return the data at positions 0, 1, 2, ...
  	$out = array();
  	foreach($index as $key)
    	{
 		$out[] = $arr[$key];
    	}	

  return $out;	
 }
//fill array
$arychairs= range(1,100);
$pass1= count_chairs_even($arychairs);
$pass2= count_chairs_even($pass1);
$pass3= count_chairs_odd($pass2);
$pass4= count_chairs_odd($pass3);
$pass5= count_chairs_odd($pass4);
$pass6= count_chairs_even($pass5);
$pass7= count_chairs_odd($pass6);
echo "<pre>" . "Pass1" ." ";
  print_r($pass1);
echo "</pre>";

echo "<pre>". "Pass2" . " ";
  print_r($pass2);
echo "</pre>";

echo "<pre>". "Pass3" . " ";
  print_r($pass3);
echo "</pre>";
echo "<pre>". "Pass4" . " ";
  print_r($pass4);
echo "</pre>";
echo "<pre>". "Pass5" . " ";
  print_r($pass5);
echo "</pre>";
echo "<pre>". "Pass6" . " ";
  print_r($pass6);
echo "</pre>";
echo "<pre>". "Pass7" . " ";
  print_r($pass7);
echo "</pre>";
?>
---------

Pass1 Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
    [4] => 10
    [5] => 12
    [6] => 14
    [7] => 16
    [8] => 18
    [9] => 20
    [10] => 22
    [11] => 24
    [12] => 26
    [13] => 28
    [14] => 30
    [15] => 32
    [16] => 34
    [17] => 36
    [18] => 38
    [19] => 40
    [20] => 42
    [21] => 44
    [22] => 46
    [23] => 48
    [24] => 50
    [25] => 52
    [26] => 54
    [27] => 56
    [28] => 58
    [29] => 60
    [30] => 62
    [31] => 64
    [32] => 66
    [33] => 68
    [34] => 70
    [35] => 72
    [36] => 74
    [37] => 76
    [38] => 78
    [39] => 80
    [40] => 82
    [41] => 84
    [42] => 86
    [43] => 88
    [44] => 90
    [45] => 92
    [46] => 94
    [47] => 96
    [48] => 98
    [49] => 100
)

Pass2 Array
(
    [0] => 4
    [1] => 8
    [2] => 12
    [3] => 16
    [4] => 20
    [5] => 24
    [6] => 28
    [7] => 32
    [8] => 36
    [9] => 40
    [10] => 44
    [11] => 48
    [12] => 52
    [13] => 56
    [14] => 60
    [15] => 64
    [16] => 68
    [17] => 72
    [18] => 76
    [19] => 80
    [20] => 84
    [21] => 88
    [22] => 92
    [23] => 96
    [24] => 100
)

Pass3 Array
(
    [0] => 4
    [1] => 12
    [2] => 20
    [3] => 28
    [4] => 36
    [5] => 44
    [6] => 52
    [7] => 60
    [8] => 68
    [9] => 76
    [10] => 84
    [11] => 92
    [12] => 100
)

Pass4 Array
(
    [0] => 4
    [1] => 20
    [2] => 36
    [3] => 52
    [4] => 68
    [5] => 84
    [6] => 100
)

Pass5 Array
(
    [0] => 4
    [1] => 36
    [2] => 68
    [3] => 100
)

Pass6 Array
(
    [0] => 36
    [1] => 100
)

Pass7 Array
(
    [0] => 36
    [1] => 
)

jrough

maybe it does work after all. i found the bug. You cannot echo $val for some reason. if I take it off then it works but I don't know what the final value is.

leatherback

ok, a last try; I removed the errors from earlier script, and now come to this:


<?php

function dropthem($var, $remove)
  {
  $new = array();
  foreach($var as $val)
    {
    if($remove)
      {
      $remove = false;
      }
    else
      {
      $remove = true;
      $new[] = $val;
      echo $val."<br />";
      }
    }
  echo "--------------". count($new) . "--------------<br />";
  if(count($new) >	 0)
    {
    dropthem($new, $remove);
	}
  }

//fill array
$arychairs= range(1,100);

dropthem($arychairs, true); 

?>

jrough

The last chair is 72 :-) Thanks, I did learn a lot.