RabbitFarm

The examples used here are from the weekly challenge problem statement and demonstrate the working solution.

Part 1

You are given a positive integer $N less than or equal to 255. Write a script to swap the odd positioned bits with the even positioned bits and print the decimal equivalent of the new binary representation.

Solution

use strict;
use warnings;
sub swap_bits{
    my($n) = @_;
    my $bits = substr(unpack("B32", pack("N", shift)), 24, 8);
    my @bits = split(//, $bits);
    for(my $i = 0; $i < @bits; $i += 2){
        @bits[$i, $i + 1] = @bits[$i + 1, $i]; 
    }  
    my $swapped_decimal = unpack("N", pack("B32", substr("0" x 32 . join("", @bits), -32)));
    return $swapped_decimal; 
}

MAIN:{
    my $N;
    $N = 101; 
    print swap_bits($N) . "\n";
    $N = 18; 
    print swap_bits($N) . "\n";
}   

Sample Run

$ perl perl/ch-1.pl
154
33

Notes

This code re-uses much of the code from last week's challenge solution. The only difference here is the for loop which swaps the even/odd bits.

Part 2

You are given time $T in the format hh:mm. Write a script to find the smaller angle formed by the hands of an analog clock at a given time.

Solution

use strict;
use warnings;
sub clock_angle{
    my($h, $m) = split(/:/, $_[0]);
    my $angle = abs(0.5 * (60 * $h - 11 * $m)); 
    $angle = 360 - $angle if $angle > 180; 
    return $angle;
}

MAIN:{
    my $T;
    $T = "03:10";  
    print clock_angle($T) . "\n";  
    $T = "04:00";  
    print clock_angle($T) . "\n";  
}

Sample Run

$ perl perl/ch-1.pl
35
120

Notes

Perhaps not a whole lot going on here: the time is broken into hour and minute parts and then the angle is computed directly from those values.

References

Challenge 120