程序員的算法趣題Perl版（三）

第七題

將日期寫成YYYYMMDD的形式，然後轉換成二進制，並逆序排列，然後再轉換成十進制，如果與之前的日期相等則正確。查找1970-01-01到2020-07-24之間正確的日期。

#! perl

#20171108

use Date::Parse;
use strict;

my $startTime = "1 Jan 1970";
my $endTime = "24 Jul 2020";

my $startStamp = str2time($startTime);
my $endStamp = str2time($endTime);

for(my $i = $startStamp; $i <= $endStamp; $i = &nextDay($i)) {

  &isRight($i);
}

sub nextDay {

    my $date = @_[0];
    my $dateNext = $date + 86400;
    return $dateNext;
}

sub isRight {

    my $date = @_[0];

    my($sec,$min,$hour,$day,$mon,$year) = localtime($date);   
    $mon++;$year += 1900;  
    my $date_now = sprintf("%04d%02d%02d",$year,$mon,$day);

    my $dateBin = sprintf("%b", $date_now);

    my $dateBinRev = reverse $dateBin;

    my $dateDnow = oct('0b' . $dateBinRev);

    if($date_now eq $dateDnow) {

        print $date_now, "\n";
    } 

    return 0; 
}

第八題

機器人可以前後左右移動，每次移動一步，不可以重複到達同一點。比如連續移動3次，則一共有36中路徑。
求：連續移動12次，有多少種路徑。

#!perl

#20171113

use strict;

# The 4 directions
my %direction = ('up' => '(0,1)',
                'down' => '(0,-1)',
                'left' => '(-1,0)',
                'right' => '(1,0)');

# This method is used to get the total steps of something like a robot has moved, 
# the robot can only move forward, backward, left and right with one step a time. 
# And one place to go only once. 
sub forward {

    my $p = @_[0];

    my @path = @$p;

    my $step = 0;
    my $length = @path;

    # The robot can only move 12 steps;
    if($length == 13) {

        return 1;
    }

    if(@path) {

        # direction loop
        foreach(values %direction) {

            my $temp = $_;

            # forward 
            $temp = &move(@path[-1], $_);

            # check the target place whether the robot has been to it
            if(! grep {$_ eq $temp} @path) {# if not, move

                # record the place
                push @path,$temp;

                # enter the iteration process
                $step += &forward(\@path);

                # pop the lastest place when the robot has explored one path
                pop @path;
            }

        }

        return $step;
    } 
}

my @path = qw/(0,0)/;
my $pp = \@path;

my $result = &forward($pp);
print "result $result \n";

# // this method is used to change the location
sub move {

    my $src = @_[0];
    my $tar = @_[1];

    my @srcArr = split /,/, $src;

    my $src_x = substr $srcArr[0], 1;
    my $src_y = substr $srcArr[1], 0;

    my @tarArr = split /,/, $tar;
    my $tar_x = substr $tarArr[0], 1;
    my $tar_y = substr $tarArr[1], 0;

    my $res_x = $src_x + $tar_x;
    my $res_y = $src_y + $tar_y;

    my $res = "(" . $res_x . "," . $res_y . ")";

    $res;
}

這道題用到了深度遍歷算法，該算法的意思就是：一條道走到黑，撞牆之後回到上一個十字路口，換個方向繼續走，一直到走完所有的路或者達到停止條件。

ps: 英文註釋是爲了提高自己的英文寫作和閱讀水平，以後還要多多練習

第九題

沒明白題目…兩組人數均等是什麼意思？男女相等麼？男生20人，女生10人，怎麼分也不會均等啊。可能是我理解有問題。