How to create php function with output true or false given array all sequence number 1 to n

Question

please help make php function that check whether a given array of integer consists all sequence number from 1 to N. Each number can only appear once in array. Output true/false.

Answer 1

Since you say integer consists all sequence number from 1 to N. Each number can only appear once in array
That means if we compare the array with a range() then the output is true/false.
You can also include a sort in case the arrays are not sorted.

$arr1 = [2,1,3,4,5,6,6,7];
$arr2 = [1,2,3,4,5,6,7];
$arr3 = [1,3,4,5,6,7];
$arr4 = [1,5,6,7,4,3,2];

// sort arrays
sort($arr1);
sort($arr2);
sort($arr3);
sort($arr4);

$n = 7;
$range = range(1,$n);
// or $range(min($array),$n); or $range(min($array),max($array)); depedning on how you want it set up


var_dump($arr1 == $range); //false
var_dump($arr2 == $range); //true
var_dump($arr3 == $range); //false
var_dump($arr4 == $range); //true

https://3v4l.org/DMe46

---

With the added information, we can use array_intersect and count.
Array intersect returns the matching items in the array.
If we then count them we see if they match.

$arr1 = array(2,3,1,4);
$arr2 = array(2,5,3,4);
$arr3 = array(1,3,4,2,5,6,3);


$range1 = range(1,max($arr1));
$range2 = range(1,max($arr2));
$range3 = range(1,max($arr3));


var_dump(count($range1) == count(array_intersect($arr1, $range1)));
// true

var_dump(count($range2) == count(array_intersect($arr2, $range2)));
// false

var_dump(count($range3) == count(array_intersect($arr3, $range3)));
// false

https://3v4l.org/7Hdll

Answer 2

• Each number has to be an integer
• Each number has to be bigger than the previous number
• Negative number are allowed.

function testInt($my_array)
{
  $prevval = null;
  foreach ($my_array as $val) {
      if ((filter_var($val, FILTER_VALIDATE_INT)) === false) {
          return false;
      }
      if ($prevval !== null) {
          if ($val <= $prevval) {
              return false;
          }
      }
      $prevval = $val;
  }
  return true;
}

$test1 = [-1, "4", 5, 7];
$test2 = [0, 1, 2, 100];
$test3 = [1, 4, 4, 100];
$test4 = [1, 5, 4, 1000];
$test5 = [5, 6, 7, "50"];

var_dump(testInt($test1));
bool(true)
var_dump(testInt($test2));
bool(true)
var_dump(testInt($test3));
bool(false)
var_dump(testInt($test4));
bool(false)
var_dump(testInt($test5));
bool(true)