Check if the array can be sorted with a single swap of 2 elements

Question

I am trying to write a function that will check if the array can be sorted with a single swap of the values in the array.

For example: array(1,3,5,3,7) must return true, but array(1,3,5,3,4) must return false.

I tried the following code below, but I'm stuck with it:

$noOfIterations = 0;

for($x = 0; $x < count($a)-2; $x++) {

    if($a[$x] > $a[$x+1]) {
        $noOfIterations ++;
    }

}

return $noOfIterations >1; 

// The below solution helped as well.

//$arr = [1, 3, 5, 3, 7];  //[1, 3, 5, 3, 4]
$arr = [1, 3, 5, 3, 4];
$sortedArr = $arr;
sort($sortedArr);
print_r(array_intersect_assoc($arr,$sortedArr));

Answer 1

This should work for you:

(Here I first make a copy of the original array to then sort() it. After this I loop through both arrays with array_map() and look how many position has changed. With array_filter() I sort the elements out where no position has changed. Then you can simply check if 2 or more position has changed and print either FALSE or TRUE)

<?php

    $arr = [1, 3, 5, 3, 7];  //[1, 3, 5, 3, 4]
    $sortedArr = $arr;
    sort($sortedArr);

    $filtered = array_filter(
        array_map(function($v1, $v2){
            return ($v1 == $v2 ?FALSE:TRUE);
        }, $arr, $sortedArr)
    );

    var_dump(count($filtered) > 2 ? FALSE : TRUE);

?>

output:

TRUE  //FALSE

Answer 2

Execute the sort, then compare the original array with the sorted array using array_intersect_assoc().... if the difference is more than two elements, then the answer is 'no'