#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
use lib '/home/kaiyin/perl5/mylib';
 
sub BinSearch {
    my ($arrayref, $wordref) = @_;
    my @array = @$arrayref;
    my $word = $$wordref;
    my ($lo, $hi) = (0, $#array);
    while ($lo <= :w
        $hi) {
        my $try = int(($lo + $hi)/2);
        if ($array[$try] lt $word) {
            $lo = ++$try; # without increment there will be
                          # a dead loop in the 4th case,
                          # see the note at the bottem
            next
        }
        elsif ($array[$try] gt $word) {
            $hi = --$try;
            next
        }
        else {
            return $try
        }
    }
    return;
}

my @a = qw(format type ascii hex pos len binary search perl unix eof a
+rray word);
my @a = sort @a;
my $w = "len";
say "@a";
say BinSearch(\@a, \$w);

# There are only 5 cases to consider:
# * - -
# - * - trivial
# - - *
# - *
# * -   trivial
#
# Among which 2 are trivial, that is to say 
# $array[$try] will immediately match $word

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Binary search algorithm.

In reply to Binary search algorithm. by kindlychung

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