PHP: Number of consecutive elements in array [closed] - php

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I have been working on one problem:
Find the largest group of consecutive numbers in an array.
Say we have an array [5, 43, 4, 56, 3, 2, 44, 57, 58, 1], the biggest group of consecutive numbers in this array is 5 (1, 2, 3, 4, and 5).
The solution algorithm must be time complexity of O(n).
I have solved this with the following ruby code but I am having trouble porting it to PHP as the solution requires.
arr = [8, 13, 14, 10, 6, 7, 8, 14, 5, 3, 5, 2, 6, 7, 4]
result = []
stage = []
for i in arr:
if len(stage) > 0 and i != stage[-1]+1:
if len(stage) > 1:
result.append(stage)
stage = []
stage.append(i)
print result

Answer 1

$a = [8, 13, 14, 10, 6, 7, 8, 14, 5, 3, 5, 2, 6, 7, 4];
$res = [];
$stage = [];
foreach($a as $i) {
if(count($stage) > 0 && $i != $stage[count($stage)-1]+1) {
if(count($stage) > 1) {
$res[] = $stage;
}
$stage = [];
}
$stage[] = $i;
}
print_r($res);

Answer 2

It's not O(n) but you can try this:
// Define array
$array = array(5,8,3,2,10,11,15,13,12,1,4,5,16);
// Sorting
asort($array);
$previous = null;
$result = array();
$consecutiveArray = array();
// Slice array by consecutive sequences
foreach($array as $number) {
if ($number == $previous + 1) {
$consecutiveArray[] = $number;
} else {
$result[] = $consecutiveArray;
$consecutiveArray = array($number);
}
$previous = $number;
}
$result[] = $consecutiveArray;
// Get length of each sub array
$count = array_map('count', $result);
You can get max length by max($count).
This solution gives you following array:
array(
0 => array(1,2,3,4,5)
1 => array(5)
2 => array(8)
3 => array(10,11,12,13)
4 => array(15,16)

Answer 3

Here is a python (my PHP is not too good) that does what your description asks, in o(n) if your sequence is decreasing:
lists = dict()
for i in val:
if i in lists:
continue
a = {i}
if (i + 1) in lists:
b = lists[i+1]
b.update(a)
a = b
if (i - 1) in lists:
b = lists[i-1]
# this messes up the complexity
for k in b:
lists[k] = a
a.update(b)
lists[i] = a
The idea is that lists maintain a dict of sets indexed on all the elements in the list. Whenever you encounter a new element, the previous and next sets are merged, if present.
The update operation is technically o(n), but it is not compounded by the external loop, as there can only be n insertion into sets by merging. The overall is o(n)
If the sequence is not sorted, the merge of the +1 and -1 sets gives a not-so-good complexity.