#!/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 intervals open - start with none
my %open_intervals;

# Let us rearrange the interval information
# into events consisting of a time/action
my @events;
foreach my $start (keys %interval) {
  my $end = $interval{$start};
  my $int = "[$start - $end]";
  if ($end < $start) {
    die "In interval '$int', the end is before the start?";
  }
  push @events,
    [$start, 0, sub {$open_intervals{$int}++}],
    [$end, 2, sub {delete $open_intervals{$int}}];
}
push @events, map {
  my $time = $_;
  [
    $_, 1, sub {
      my @ints = keys %open_intervals;
      print "Time $time is in intervals (@ints)\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]->();
}
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