PHP Check if a number is in sequence but with one missing - php

Question

I can find if an array of values are in sequence using:
sort($arr);
if ($arr == range($arr[0], $arr[count($arr)-1])) {
return true;
}
So anything like 1,2,3,4,5, 6,7,8 will result in true but how can I find a number in sequence but with one number missing? So the expected output would be:
2,3,5,6 = true
2,5,6,8 = false
3,6,10,16 = false
5,7,8,9,10,11 = true

Answer 1

I just checked this and it matches the outputs you expect from your original question
function skippedValue($arr) {
sort($arr);
return sizeof(array_diff(range($arr[0], $arr[count($arr)-1]), $arr)) == 1;
}
var_dump(skippedValue([2,3,5,6])); // true
var_dump(skippedValue([2,5,6,8])); // false
var_dump(skippedValue([3,6,10,16])); // false
var_dump(skippedValue([5,7,8,9,10,11])); //true
result: bool(true) bool(false) bool(false) bool(true)

Answer 2

Algorithmically rather verbose, but works:
function checkAlmostSequential(array $seq, $maxSkips = 1) {
$skipped = 0;
for ($i = 0, $num = $seq[0]; $i < count($seq); $num++) {
if ($num == $seq[$i]) {
$i++;
} else {
$skipped++;
}
if ($skipped > $maxSkips) {
return false;
}
}
return true;
}
var_dump(checkAlmostSequential([2,3,5,6])); // true
var_dump(checkAlmostSequential([2,5,6,8])); // false
var_dump(checkAlmostSequential([3,6,10,16])); // false
var_dump(checkAlmostSequential([5,7,8,9,10,11])); // true

Answer 3

Small function to verify if is sequence
function verifySequence($arr){
sort($arr);
for($i = 0; $i < sizeof($arr) - 1; $i++){
$j = $i + 1;
if( (($arr[$i] + 1) !== $arr[$j]) && (($arr[$i] + 2) !== $arr[$j])){
return false;
}
}
return true;
}

Answer 4

Having misunderstood the question initially I hope this now does as expected - not the easiest to read perhaps.
$a=[1,2,5,6];
$b=[34,35,36,37,38];
$c=[5,7,8,9,10,15];
$d=[1,3,4,5,6,8];
$e=[3,6,10,16];
$f=[2,3,5,6];
function is_semi_sequential( $a ){
rsort( $a );
$c=[];
for( $i=count( $a )-1; $i >= 0; $i-- ){
if( isset( $a[ $i ] ) && isset( $a[ $i+1 ] ) && $a[ $i ] - $a[ $i + 1 ]!=1 ) $c[]=( $a[ $i ] - $a[ $i + 1 ] );
}
return count( $c ) <= 1 && array_sum( $c ) <= 2 ? true : false;
}
echo is_semi_sequential( $a ) ? 'sequential' : 'non-sequential';
echo '<br />';
echo is_semi_sequential( $b ) ? 'sequential' : 'non-sequential';
echo '<br />';
echo is_semi_sequential( $c ) ? 'sequential' : 'non-sequential';
echo '<br />';
echo is_semi_sequential( $d ) ? 'sequential' : 'non-sequential';
echo '<br />';
echo is_semi_sequential( $e ) ? 'sequential' : 'non-sequential';
echo '<br />';
echo is_semi_sequential( $f ) ? 'sequential' : 'non-sequential';
Outputs:
non-sequential
sequential
non-sequential
non-sequential
non-sequential
sequential

Answer 5

You can check using good old for loop
function missingItemChecker($arr, $max_missing = 1){
sort($arr);
$check_arr = range($arr[0], $arr[count($arr)-1]);
$missing = 0;
$len = count($check_arr);
$j = 0;
for($i = 0; $i < $len; $i++) {
if( $check_arr[$i] !== ($arr[$j] ?? false) ){
$missing++;
} else { $j++; }
}
return $missing == $max_missing;
}
Edit: The Logic here is,
Sort to get the Minimum and Maximum in the range using sort($arr).
Create an array of the actual sequence $check_arr = range().
Maintain a count of the numbers missing with $missing.
Loop through the real sequence to and check against the input array
to get the number of the missing elements.
If the number of missing elements is equal to the max allowed missing elements, the sequence has more than 1 numbers missing, else its either complete or only one element is missing.

Answer 6

If we count items that are one value more than the previous, the total will be two less than the amount of items for sequences with only one missing member.
<?php
// Assuming zero indexed and sequential keys in input array.
function missing_only_one_incremental_value_in_sequence(array $nums)
{
$count = count($nums);
$seq_count = 0;
for($i=1; $i<$count; $i++)
if($nums[$i]==$nums[$i-1]+1)
$seq_count++;
return $seq_count == $count-2;
}
var_dump(missing_only_one_incremental_value_in_sequence([2,3,5,6]));
var_dump(missing_only_one_incremental_value_in_sequence([2,5,6,8]));
Output:
bool(true)
bool(false)
For more sample inputs and outputs see here: https://3v4l.org/PFQ5d