PHP Program to Find lost element from a duplicated array

<?php
// PHP program to find missing 
// element from same arrays 
// (except one missing element)

// Function to find missing 
// element based on binary
// search approach. arr1[] 
// is of larger size and
// N is size of it. arr1[]
// and arr2[] are assumed
// to be in same order.
function findMissingUtil($arr1, $arr2, $N)
{
    
    // special case, for only 
    // element which is
    // missing in second array
    if ($N == 1)
        return $arr1[0];

    // special case, for first
    // element missing
    if ($arr1[0] != $arr2[0])
        return $arr1[0];

    // Initialize current 
    // corner points
    $lo = 0;
    $hi = $N - 1;

    // loop until lo < hi
    while ($lo < $hi)
    {
        $mid = ($lo + $hi) / 2;

        // If element at mid indices are 
        // equal then go to right subarray
        if ($arr1[$mid] == $arr2[$mid])
            $lo = $mid;
        else
            $hi = $mid;

        // if lo, hi becomes 
        // contiguous, break
        if ($lo == $hi - 1)
            break;
    }

    // missing element will be 
    // at hi index of
    // bigger array
    return $arr1[$hi];
}

// This function mainly 
// does basic error checking
// and calls findMissingUtil
function findMissing($arr1, $arr2, 
                           $M, $N)
{
    if ($N == $M - 1)
        echo "Missing Element is "
             , findMissingUtil($arr1, 
                         $arr2, $M) ;
    else if ($M == $N - 1)
        echo "Missing Element is "
             , findMissingUtil($arr2, 
                           $arr1, $N);
    else
        echo "Invalid Input";
}

    // Driver Code
    $arr1 = array(1, 4, 5, 7, 9);
    $arr2 = array(4, 5, 7, 9);
    $M = count($arr1);
    $N = count($arr2);
    findMissing($arr1, $arr2, $M, $N);

// This code is contributed by anuj_67.
?>

<?php
// PHP program to find missing
// element from one array
// such that it has all elements
// of other array except
// one. Elements in two arrays 
// can be in any order.

// This function mainly does
// XOR of all elements
// of arr1[] and arr2[]
function findMissing($arr1, $arr2, 
                           $M, $N)
{
    if ($M != $N - 1 && $N != $M - 1)
    {
        echo "Invalid Input";
        return;
    }

    // Do XOR of all element
    $res = 0;
    for ($i = 0; $i < $M; $i++)
        $res = $res ^ $arr1[$i];
        
    for ($i = 0; $i < $N; $i++)
    $res = $res ^ $arr2[$i];
    echo "Missing element is ", $res;
}

    // Driver Code
    $arr1 = array(4, 1, 5, 9, 7);
    $arr2 = array(7, 5, 9, 4);
    $M = sizeof($arr1);
    $N = sizeof($arr2);

    findMissing($arr1, $arr2, $M, $N);

// This code is contributed by aj_36
?>