Zig-zag scan an N x N array

Question

I have a simple array. The array length always has a square root of an integer. So 16, 25, 36 etc.

$array = array(\'1\', \'2\', \'3\', \'4\' ... \'25\');
         


        

Answer 1

One more PHP solution, using just for and if, traverses array only once

function waveSort(array $array) {

    $elem = sqrt(count($array));

    for($i = 0; $i < $elem; $i++) {
        $multi[] = array_slice($array, $i*$elem , $elem);
    }

    $new = array();
    $rotation = false;
    for($i = 0; $i <= $elem-1; $i++) {
        $k = $i;
        for($j = 0; $j <= $i; $j++) {
            if($rotation)
                $new[] = $multi[$k][$j];
            else
                $new[] = $multi[$j][$k];
            $k--;
        }   
        $rotation = !$rotation;
    }

    for($i = $elem-1; $i > 0; $i--) {
        $k = $elem - $i;

        for($j = $elem-1; $j >= $elem - $i; $j--) {

            if(!$rotation)
                $new[] = $multi[$k][$j];
            else
                $new[] = $multi[$j][$k];
            $k++;
        }   
        $rotation = !$rotation;
    }

    return $new;
}

$array = range(1, 25);
$result = waveSort($array);
print_r($result);

$array = range(1, 36);
$result = waveSort($array);
print_r($result);

Here it is in action

Answer 2

Here's mine.

function waveSort(array $array) {
  $dimension = pow(count($array),0.5);
  if((int)$dimension != $dimension) {
    throw new InvalidArgumentException();
  }

  $tempArray = array();
  for($i = 0; $i < $dimension; $i++) {
    $tempArray[] = array_slice($array,$i*$dimension,$dimension);
  }

  $returnArray = array();

  for($i = 0; $i < $dimension * 2 -1; $i++) {
    $diagonal = array();

    foreach($tempArray as $x => $innerArray) {
      if($i - $x >= 0 && $i - $x < $dimension) {
        $diagonal[] = $innerArray[$i - $x];
      }
    }

    if($i % 2 == 1) {
      krsort($diagonal);
    }

    $returnArray = array_merge($returnArray,$diagonal);

  }

  return $returnArray;

}

Usage:

<?php
$a = range(1,25);
var_dump(waveSort($a));

Output

array(25) {
  [0]=>
  int(1)
  [1]=>
  int(6)
  [2]=>
  int(2)
  [3]=>
  int(3)
  [4]=>
  int(7)
  [5]=>
  int(11)
  [6]=>
  int(16)
  [7]=>
  int(12)
  [8]=>
  int(8)
  [9]=>
  int(4)
  [10]=>
  int(5)
  [11]=>
  int(9)
  [12]=>
  int(13)
  [13]=>
  int(17)
  [14]=>
  int(21)
  [15]=>
  int(22)
  [16]=>
  int(18)
  [17]=>
  int(14)
  [18]=>
  int(10)
  [19]=>
  int(15)
  [20]=>
  int(19)
  [21]=>
  int(23)
  [22]=>
  int(24)
  [23]=>
  int(20)
  [24]=>
  int(25)
}