Determining overlapping time ranges based on day of the week - php

Question

I have an array of time ranges like this:-
$events = array(
array("Monday", '19:00:00', '19:30:00', 0),
array("Monday", '19:10:00', '19:40:00', 0),
array("Tuesday", '19:10:00', '19:40:00', 0),
array("Wednesday", '19:10:00', '19:40:00', 0),
array("Monday", '19:30:00', '19:50:00', 0),
);
I am using bubble sort on the array:-
for($i = 0; $i < (count($events) - 1); $i++)
{
for($j = 1; $j < (count($events) - i - 1); $j++)
{
if($events[$i][0] < $events[$j][0])
{
if ($events[$j] > $events[($j + 1)])
{
$swap = $events[$j];
$events[$j] = $events[($j + 1)];
$events[($j + 1)] = $swap;
}
}
}
}
The result comes like this:-
Array (
[0] => Array (
[0] => Monday
[1] => 19:00:00
[2] => 19:30:00
[3] => 0)
[1] => Array (
[0] => Monday
[1] => 19:10:00
[2] => 19:40:00
[3] => 0)
[2] => Array (
[0] => Monday
[1] => 19:30:00
[2] => 19:50:00
[3] => 0)
[3] => Array (
[0] => Tuesday
[1] => 19:10:00
[2] => 19:40:00
[3] => 0)
[4] => Array (
[0] => Wednesday
[1] => 19:10:00
[2] => 19:40:00
[3] => 0)
)
Now I need to strike out those time ranges which overlap on a specific day.
Like this:
Array (
[0] => Array (
[0] => Monday
[1] => 19:00:00
[2] => 19:30:00
[3] => 1)
[1] => Array (
[0] => Monday
[1] => 19:10:00
[2] => 19:40:00
[3] => 1)
[2] => Array (
[0] => Monday
[1] => 19:30:00
[2] => 19:50:00
[3] => 1)
[3] => Array (
[0] => Tuesday
[1] => 19:10:00
[2] => 19:40:00
[3] => 0)
[4] => Array (
[0] => Wednesday
[1] => 19:10:00
[2] => 19:40:00
[3] => 0)
)
The ones which are [3] => 1, denote there is a time overlap conflict.
How can I proceed?
I tried to use this solution, but got no luck. Besides, mine has a day of week.

Answer 1

I had a little play and this is what I came up with. It preserves the original order of the $events array as textual days don't sort well (Friday would come before Wednesday etc). A bit brute force, not optimised or properly tested, but hope it's useful for ideas.
foreach ($events as $event_id=>$event) {
$days[$event[0]][]=[$event_id,$event[1],$event[2]];
}
foreach ($days as $dayevents) {
if (count($dayevents)>1) {
foreach ($dayevents as $dayevent1) {
foreach ($dayevents as $dayevent2) {
if ((($dayevent1[1]>$dayevent2[1]) and ($dayevent1[1]<$dayevent2[2])) or
(($dayevent1[2]>$dayevent2[1]) and ($dayevent1[2]<$dayevent2[2]))) {
$events[$dayevent1[0]][3]=1;
$events[$dayevent2[0]][3]=1;
}
}
}
}
}

Answer 2

$events = array(
array("Monday", '19:00:00', '19:30:00', 0),
array("Monday", '19:10:00', '19:40:00', 0),
array("Tuesday", '19:10:00', '19:40:00', 0),
array("Wednesday", '19:10:00', '19:40:00', 0),
array("Monday", '19:30:00', '19:50:00', 0),
);
$combined = array();
// first we collect all intervals for the given day
foreach($events as $record)
{
$combined[$record[0]][] = array(
$record[1], $record[2], 0
);
}
// then for each day we look if there are overlaps
foreach($combined as $day => &$intervals)
{
$len = count($intervals);
// we compare each interval with each of the rest intervals for the same day
foreach($intervals as $i => &$interval_1)
{
// we convert the start/end times of the interval A to an integer
$begin_1 = str_replace(':','',$interval_1[0]);
$end_1 = str_replace(':','',$interval_1[1]);
for($k = $i + 1; $k < $len; $k++)
{
// we convert the start/end times of the interval B to an integer
$begin_2 = str_replace(':','',$intervals[$k][0]);
$end_2 = str_replace(':','',$intervals[$k][1]);
// we compute the overlap of the 2 intervals
$overlap = max(0,$end_1 - $begin_1 - max(0,$end_1 - $end_2) - max(0,$begin_2 - $begin_1));
if($overlap)
{
$interval_1[2]++; // we increase the counter of interval A
$intervals[$k][2]++; // we increase the counter of interval B
}
}
}
}

Answer 3

<?php
$events = array(
array("Monday", '19:00:00', '19:10:00'),
array("Monday", '19:05:00', '19:20:00'),
array("Tuesday", '19:10:00', '19:40:00'),
array("Wednesday", '19:10:00', '19:40:00'),
array("Monday", '19:15:00', '19:30:00'),
);
function convertToSeconds($time){
$time = explode(":",$time);
return intval($time[0]) * 3600 + intval($time[1]) * 60 + intval($time[2]);
}
$time_ranges = [];
$hold_dates = [];
for($i=0;$i<=86401;++$i){
$time_ranges[] = 0;
$hold_dates[$i] = [];
}
$time_range_for_week = [];
$week_days = ['monday' ,'tuesday','wednesday','thursday','friday','saturday','sunday'];
foreach($week_days as $day){
$time_range_for_week[$day] = [
'hold_dates' => $hold_dates,
'time_range' => $time_ranges
];
}
foreach($events as &$data){
$start_time = convertToSeconds($data[1]);
$end_time = convertToSeconds($data[2]);
$time_range_for_week[strtolower($data[0])]['hold_dates'][$start_time][] = &$data;
$time_range_for_week[strtolower($data[0])]['hold_dates'][$end_time][] = &$data;
$time_range_for_week[strtolower($data[0])]['time_range'][$start_time] += 1;
$time_range_for_week[strtolower($data[0])]['time_range'][$end_time + 1] -= 1;
}
foreach($time_range_for_week as $day_name => &$day_data){
$sum = 0;
foreach($day_data['time_range'] as $time => $value){
$sum += $value;
if($sum > 1 && count($day_data['hold_dates'][$time]) > 0){
foreach($day_data['hold_dates'][$time] as &$each_event){
$each_event[3] = 1;
}
}
}
}
print_r($events);
Demo: https://3v4l.org/JeGdR
Algorithm:
This is rather simple and efficient than basic brute force.
To find out collisions between times, we first make an array of size 86400 for each day. 86400 because it is no. of seconds(24*60*60) for a day(like Monday or Tuesday etc).
The array looks like this for a particular day(like Monday or Tuesday etc):
Structure:
Array
(
[monday] => Array
(
[hold_dates] => Array
(
[],[],[],... till 86400
),
[time_range] => Array
(
[],[],[],... till 86400
),
),
[tuesday] => Array(
...
),
...
)
In the hold_dates key for a day, we are just going to have our array values at the start time and end times positions. Here start time is the 1st position(0-based indexing) in array("Monday", '19:10:00', '19:40:00', 0) and end time is 2nd position in array("Monday", '19:10:00', '19:40:00', 0). In the code, the lines look like:
Code:
$time_range_for_week[strtolower($data[0])]['hold_dates'][$start_time][] = &$data;
$time_range_for_week[strtolower($data[0])]['hold_dates'][$end_time][] = &$data;
The & is used for syncing updates with actual $events array, so it's a pass by reference.
The time_range will just hold integer values and those integer values as explained below.
Let's consider intervals like below:
[2,7],
[4,9],
[6,10]
We have a timeline like below:
1 2 3 4 5 6 7 8 9 10 11 // these are seconds from 1 to 11
+1 -1
+1 -1
+1 -1
1 1 2 2 3 3 2 2 1 0
In the above diagram, for each date's start time, we add +1, and -1 to it's end time + 1. This means that, when we iterate from 1 to 11 and keep summing values, if we find any date's start time or end time having a sum > 1, we found there is a collision and we need to set it's value to 1.
We do the same in the above code. Here, the space used for this code is 86400 * 7 = 604800, which is constant space O(1) since this does not depend upon size of $events.
Time complexity is again the constant iterations 86400 * 7 = 604800 + looping twice through each element in $events, which makes it O(n) where n is size of $events.