algorithm - 寻找一种将宽度分配给列的算法

Question

我想将数据库表打印到 STDOUT。如果表格宽度大于屏幕宽度，我想以相同的百分比剪切每个列(除非表格宽度已达到 min_width)，直到表格适合屏幕。我试图用发布的子程序解决这个问题。有人知道解决这个问题的更短更优雅的算法吗？

sub cal_size {
    my ( $maxcols, $ref ) = @_;         
    # $maxcols => screen width
    # $ref => ref to an AoA; holds the table
    my ( $max ) = cal_tab( $ref );
    # $max => ref to an array; holds the length of the longest string of each column
    # $tab = 2;
    if ( $max and @$max ) {
        my $sum = sum( @$max ) + $tab * @$max; 
        $sum -= $tab;
        my @max_tmp = @$max;
        my $percent = 0;
        while ( $sum > $maxcols ) {
            $percent += 0.5;
            if ( $percent > 99 ) {
                return;
            }
            my $count = 0;

            for my $i ( 0 .. $#max_tmp ) {
                # $min_width => columns width should not be less than $min_width if possible 
                next if $min_width >= $max_tmp[$i]; 
                # no need to cut if the column width id less than min_width
                next if $min_width >= minus_x_percent( $max_tmp[$i], $percent ); 
                # don't cut if column width become less than min_width 
                $max_tmp[$i] = minus_x_percent( $max_tmp[$i], $percent );
                $count++;
                last if $sum <= $maxcols;   
            }
            $min_width-- if $count == 0 and $min_width > 1; 
            # if no cuts but $sum > $maxcols reduce $min_width
            $sum = sum( @max_tmp ) + $tab * @max_tmp; 
            $sum -= $tab;
        }
        my $rest = $maxcols - $sum;
        while ( $rest > 0 ) { # distribute the rest
            my $count = 0;
            for my $i ( 0 .. $#max_tmp ) {
                if ( $max_tmp[$i] < $max->[$i] ) {
                    $max_tmp[$i]++;
                    $rest--;
                    $count++;
                    last if $rest < 1;
                }
            } 
            last if $count == 0;
            last if $rest < 1;
        }
        $max = [ @max_tmp ] if @max_tmp;
    }
    return $max;
}


sub minus_x_percent {
    my ( $value, $percent ) = @_;
    return int $value - ( $value * 1/100 * $percent );
}

Answer 1

如果不是字段宽度的下限，这个问题会很简单。一旦字段不能再变小，只有较大的字段才有资格进行缩放，因此计算会有所不同，具体取决于是所有字段、没有字段还是部分字段已缩小到其限制。

缩放比例有几个带，每个唯一字段宽度一个。由于字段按比例缩小，其中最小的字段将最先达到最小字段大小限制。之后只有大于最小尺寸的列才能进一步缩小，直到第二小的也达到限制。

这一直持续到所有列都达到其最小大小，之后可用空间在列之间平均分配。

该程序实现了该算法的计算，我认为它可以满足您的要求。

请注意，返回的字段宽度是浮点值，您必须根据需要对其进行四舍五入。

use strict;
use warnings;

use List::Util 'max';

my $min_col_width = 10;
my $tab = 2;

my $widths = recalc_widths(80, [ 10, 15, 20, 25, 30 ]);
print join '  ', map sprintf('%.3f', $_), @$widths;
print "\n";

sub recalc_widths {

  my ($target, $widths) = @_;
  $target -= (@$widths - 1) * $tab;

  my @sorted_widths = sort { $a <=> $b } @$widths;

  my $num_limited = 0;
  my $adjustable_total_width = 0;
  $adjustable_total_width += $_ for @sorted_widths;

  while (@sorted_widths) {

    my $boundary = $sorted_widths[0];

    my $scale = ($target - $num_limited * $min_col_width) / $adjustable_total_width;

    if ($boundary * $scale >= $min_col_width) {
      return [ map max($_ * $scale, $min_col_width), @$widths ];
    }

    while (@sorted_widths and $sorted_widths[0] == $boundary) {
      shift @sorted_widths;
      $adjustable_total_width -= $boundary;
      $num_limited++;
    }
  }

  return [ ($target / $num_limited) x $num_limited ];
}

输出

10.000  10.333  13.778  17.222  20.667