如何在PHP中交换多维数组的矩阵主对角元素

Question

I want to swap only main diagonal elements of matrix of an multidimensional array like below

Before swapping

 11  12 13  14  15
 21  22 23  24  25
 31  32 33  34  35
 41  42 43  44  45
 51  52 53  54  55

After swapping -it should be
 55 12  13  14  15
 21 44  23  24  25
 31 32  33  34  35
 41 42  43  22  45
 51 52  53  54  11

What i did is - i am able to get diagonal elements as below, its quite simple but i cannot proceed further

<?php

  $array = array (
        array( '11','12','13','14','15'),
        array( '21','22','23','24','25'),
        array( '31','32','33','34','35'),
        array( '41','42','43','44','45'),
        array( '51','52','53','54','55')
    );

  foreach ( $array as $key => $val ) {

      print "<br>".$val[$key];

   }
?>  

Answer 1

It's sounds like you're a bit lost. This isn't too hard, I suggest you dividing it into smaller problems which might make it easier for you to deal with.

1. First create a function to get the diagonal array based on matrix size

   suggestion You have a nxn matrix represented by 2d array a[i][j] then (pseudo code):

    while i < n do: diagonal << a[i][j] i,j+=1 

2. Then, create a swap function for the diagonal, there's reverse_array function in PHP that might help.

3. Finally, when having reversed-diagonal calculated you can just print the old array and swap its diagonal with the new one.

There are shorter ways and much efficient ones, but in my opinion this how you should do it so next time you're facing this kind of problem you'll know the flow.

Answer 2

I think what you are missing is being able to access your $array by both 'x' and 'y' coordinates by: $array[$x][$y].

<?php
  $array = array (
        array( '11','12','13','14','15'),
        array( '21','22','23','24','25'),
        array( '31','32','33','34','35'),
        array( '41','42','43','44','45'),
        array( '51','52','53','54','55')
    );
print_array($array);
echo "--------------\n";

//swap 
for( $i=0; $i<2; $i++ ){
  $temp= $array[$i][$i];
  $array[$i][$i]= $array[4-$i][4-$i];
  $array[4-$i][4-$i]=$temp;
}
print_array($array);

function print_array( $array )
{
  for($i=0;$i<5;$i++)
  {
    for($j=0;$j<5;$j++)
       echo $array[$i][$j]." ";
    echo "\n";
  }
}
?>

I'll let you figure out why the swap loop has $i<2 in it whereas the print loop has $i<5 :)

Yours, TonyWilk

Answer 3

Here is working example ;)

<?php

$array = array (
            array( '11','12','13','14','15','16'),
            array( '21','22','23','24','25','26'),
            array( '31','32','33','34','35','36'),
            array( '41','42','43','44','45','46'),
            array( '51','52','53','54','55','56'),
            array( '61','62','63','64','65','66')
        );

//print "<pre>";
//print_r($array); exit;

$cnt = count($array);

$i = 0; $j = count($array) - 1;

foreach ( $array as $key => $val ) {

    $newArr[$i][$j] = $val[$key];

    $j--; $i++;

}


$reversed = array_reverse($newArr);

$result = array_replace_recursive($array,$reversed);

matrix($array,$cnt);

print "=======================<br><br>";

matrix($result,$cnt);

function matrix( $result,$cnt )
{
    for($i=0;$i<$cnt;$i++)
    {
        for($k=0;$k<$cnt;$k++)
        {
            echo $result[$i][$k]." ";
            echo "<br>";
        }
    }
}

?>