#!/usr/bin/perl -w
use strict;

# The original data structure
my %interval = qw(
  5     50
  20    30
  70    90
  120   130
);

# The times
my @times = qw(4 9 30 98 125 500);

# Current nesting depth
my $depth =  0;

# Let us rearrange the interval information
# into events consisting of a time/action
my @events = map {[$_, 0, sub {++$depth}]} keys %interval;
push @events, map {[$_, 2, sub {--$depth}]} values %interval;
push @events, map {
  my $time = $_;
  [$_, 1, sub {print "Time $time is at depth $depth\n"}]
} @times;

# Sort it and read out the answer: 
foreach my $event (
  sort {
    $a->[0] <=> $b->[0] or $a->[1] <=> $b->[1]
  } @events
) {
  $event->[2]->();
}