Learn Perl from Scratch/

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Solution Review: Print a Matrix

Solution Review: Print a Matrix

Let's go over the solution review of the challenge given in the previous lesson.

We'll cover the following...

Let’s look at the solution first before jumping into the explanation:

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Perl
sub printMat {
  $n = @_[0];
  @arr=();
  for ($i=0;$i<$n;$i++) {
    for ($j=0;$j<$n;$j++){
      if ($i==$j){	        	# if row=column=> fill the matrix with 0
        $arr[$i][$j] = 0;
      }
      elsif($i>$j){			# if row>columns=> fill matrix with -1
        $arr[$i][$j] = -1;
      }
      else {					# if row<columns=> fill matrix with 1
        $arr[$i][$j] = 1;
      }
    }
  }
  for ($i=0;$i<$n;$i++) {
    for ($j=0;$j<$n;$j++){
sub printMat {
  $n = @_[0];
  @arr=(); 
  for ($i=0;$i<$n;$i++) {
    for ($j=0;$j<$n;$j++){
      if ($i==$j){	        	# if row=column=> fill the matrix with 0
        $arr[$i][$j] = 0;
      }
      elsif($i>$j){			# if row>columns=> fill matrix with -1
        $arr[$i][$j] = -1;
      }
      else {					# if row<columns=> fill matrix with 1
        $arr[$i][$j] = 1;
      }
    }
  }
  for ($i=0;$i<$n;$i++) {
    for ($j=0;$j<$n;$j++) {
      print $arr[$i][$j]." ";
    }
    print "\n";
  }
}    }
    print "\n";
  }
}
printMat(4);

Explanation

We want to create a matrix (two-dimensional array) of size passed from the printMat subroutine. @_[0] is used to get the size as this is the only argument passed to this subroutine. The elements in the array are stored using the following conditions:

  • if $i is equal to $j then store 0, handling diagonal
  • else if $i is greater than $j then store -1, handling all elements below diagonal
  • else store 1, handling all elements above diagonals

We use a nested for loop to print all elements of the array.