PHP 合并有序数组

<?php
//两个有序数组合并
$arr1 = [1,5,7,44,66,89]; $arr2 = [4,5,6,88,99,105,111];
$arr3 = [];
$l1 = count( $arr1 );
$l2 = count( $arr2 );
$i = $j = 0;
while(true){
    if( !isset( $arr1[$i] ) ){
        for( $j; $j <$l2; $j++ ){
            $arr3[] = $arr2[$j];
        }
        break;
    }
    if( !isset( $arr2[$j] ) ){
        for( $i; $j <$l1; $i++ ){
            $arr3[] = $arr1[$i];
        }
        break;
    }

    while( isset( $arr2[$j] ) && ( $arr1[$i] > $arr2[$j] ) ){
       $arr3[] = $arr2[$j];
       $j++;
    }
    
    while(  isset( $arr1[$i] ) && ( $arr1[$i] < $arr2[$j] ) ){
        $arr3[] = $arr1[$i];
        $i++;
    }
    
    if(  isset( $arr1[$i] ) &&  isset( $arr1[$i] ) && ( $arr1[$i] ==  $arr2[$j] ) ){
        $arr3[] = $arr1[$i];
        $i++;$j++;
    }
 
}
print_r( $arr3 );

?>