#!/usr/bin/perl use strict; use warnings; my %distances = ( 100 => 'London', 200 => 'Paris', 300 => 'Rome', 600 => 'Berlin' ); my @distances = sort {\$a<=>\$b} keys %distances; sub make_btree { my \$first = shift; my \$nof = shift; if ( \$nof == 1 ) { return { Value => \$distances[\$first] }, } else { my \$m = int(\$nof/2); my \$val = ( \$distances[\$first+\$m-1] + \$distances[\$first+\$m] )/2; return { Value => \$val, Left => make_btree(\$first, \$m), Right => make_btree(\$first+\$m, \$nof-\$m), } } } my \$BTREE = make_btree(0, scalar @distances); #use Data::Dumper; #print Dumper( \$BTREE ); sub closest_city { my \$key = shift; my \$btree = \$BTREE; while ( exists \$btree->{Left} ) { my \$v = \$btree->{Value}; \$btree = \$btree->{ \$key<\$v ? 'Left' : 'Right' } } \$distances{ \$btree->{Value} }; } print q{closest_city(5)="}, closest_city(5), qq{"\n}; print q{closest_city(149)="}, closest_city(149), qq{"\n}; print q{closest_city(150)="}, closest_city(150), qq{"\n}; print q{closest_city(203)="}, closest_city(203), qq{"\n}; print q{closest_city(290)="}, closest_city(290), qq{"\n}; print q{closest_city(500)="}, closest_city(500), qq{"\n}; print q{closest_city(5000)="}, closest_city(5000), qq{"\n}; ##```## closest_city(5)="London" closest_city(149)="London" closest_city(150)="Paris" closest_city(203)="Paris" closest_city(290)="Rome" closest_city(500)="Berlin" closest_city(5000)="Berlin" ##``````## 250 / \ 150 450 / | | \ 100 200 300 600 | | | | London Paris Rome Berlin ```