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#!/Users/colincrain/perl5/perlbrew/perls/perl-5.32.0/bin/perl
#
# what-angle-we-at.pl
#
# Clock Angle
# Submitted by: Mohammad S Anwar
# 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.
#
# HINT: A analog clock is divided up into 12 sectors. One sector
# represents 30 degree (360/12 = 30).
#
# Example
# Input: $T = '03:10'
# Output: 35 degree
#
# The distance between the 2 and the 3 on the clock is 30 degree.
# For the 10 minutes i.e. 1/6 of an hour that have passed.
# The hour hand has also moved 1/6 of the distance between the 3 and the
# 4, which adds 5 degree (1/6 of 30).
# The total measure of the angle is 35 degree.
#
# Input: $T = '04:00'
# Output: 120 degree
# method:
# Rolex wristwatches are known for their "sweep" second hand
# movement; that is to say the hand does not move incrementally,
# once a second, from one pip to the next, but rather is seen to
# move in a continuous flow around the dial. This action is
# remarkably difficult to achieve in a mechanical movement where the
# fundamental timekeeping period is based on an oscillating
# vibration, such as a pendulum. In fact it is ultimately
# illusionary, based on a rapidly moving pendulum buffered by
# springs to appear more fluid.
#
# With the introduction of inexpensive, accurate electric motors
# much of the panache of the sweep hand has gone away, and the Rolex
# has had to rely more on its rugged good looks and maybe the notion that
# it's body is machined from a giant block of gold. But I digress.
# In a pendulum-driven clock movement the action is commonly
# designed to move with a two-second period: one across, and one
# back. This can be precisely tuned by adjusting the length of the
# pendulum arm, and forms the basis of all the timekeeping: each
# half-swing is one tick, 60 of these comprise a minute, and three
# thouand six hundred to an hour.
#
# It's not hard to make a clock with a sweep minute hand, where the
# hand makes one revolution per hour in as many increments as the
# pendulum allows. But this is not always advantagous: in a clock
# without a second hand, such as one would find in a clock-tower,
# having the minute hand fall between marks leads to ambiguity in
# reading. One person may see 43 minutes past the hour, another 42.
# It is often more desirable to have an intenal mechanism rachet
# along counting pendulum swings on a gear, and only once a
# revolution have a pin engage a mechanism and move the minute hand
# one place. In this way the clock hand stays at 42 until the moment
# arrives, when in moves all at onece to 43 and remains for another
# minute until it moves again.
#
# On the other, other hand, no mechanical clock does this for the hour
# hand. We go about our day and normally deal with time in a finer
# granularity than the hour, and hence knowing that it's somewhere
# between 1 and 2 is useful information in itself to know.
#
# So ignoring the second hand, in just the hours and minutes of many
# common clocks we have
# two modes of moving the hand: continuous and discrete. With
# respect to an angle swept from midnight or noon, the minute hand
# will have moved six degrees every minute, always. As without
# further information we have no
# idea how many seconds have elapsed since the last minute tick
# we cannot improve on this
# calculation even if we wanted to.
#
# For the hours, back to one of our previous other hands,
# the hand moves a set amount for
# each hour, but also takes a submovement between the pips based on
# dividing the interval between two hour points into 60 minutes. The
# final sweep amount for the hand at any given time will be the sum
# of the two partial motions.
#
# © 2021 colin crain
## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ## ##
use warnings;
use strict;
use utf8;
use feature ":5.26";
use feature qw(signatures);
no warnings 'experimental::signatures';
my $timestr = shift // qw ( 9:49);
my ($h, $m) = $timestr =~ /(\d?\d):(\d\d)/;
$h %= 12;
my $mdeg = $m * 6;
my $hdeg = $h * 30 + $m * 0.5;
my $ang = abs( $hdeg - $mdeg );
$ang = 360 - $ang if $ang > 180;
say "time: $timestr";
say "$ang degrees";
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