PHP Check if number is smaller than array element values - php

Question

This seems really simple but I can't figure out the cleanest way to do it...
Basically I have a sorted Array with numbers like this:
$array1 = [3, 7, 12, 63, 120, 512, 961];
What I need to do is check each element of the array against a number which can be like this:
$number = 320;
And I need to get the element which is next to the number in this example it would be 120 because 120 < $number < 512.
Well, my way approach which kinda works is pretty messy I think:
foreach ($i = 0; $i < count($array1); $i++) {
if ($array[$i] < $number) {
// echo "do nothing, elements are smaller than number
} else {
if ($flag == true) {
// echo "elements are not smaller anymore and flag is set"
$getValue = $array[$i-1]; // last element which was smaller
$flag == false;
}
}
}
Another problem is, I need to cover the cases if $number is smaller than the smallest element of the array or if its larger than the largest element of the array. For that case I create another Variable $t and check it with the length of the array in each iteration
$t = 0;
$len = count($array1);
// if element bigger than number and first iteration
if ($array[$i] > $number && $t == 0) {
}
$t += 1;
I left the foreach loop out here but as you can probably see it gets really long and its certainly not clean. How can it be done better?

Answer 1

As it is an sorted array you are working with then i recommend you to implement binary search algorithm which has O(log(n)) in time complexity .
int binary_search(int A[], int key, int imin, int imax)
{
// continue searching while [imin,imax] is not empty
while (imin <= imax)
{
// calculate the midpoint for roughly equal partition
int imid = midpoint(imin, imax);
if(A[imid] == key)
// key found at index imid
return imid;
// determine which subarray to search
else if (A[imid] < key)
// change min index to search upper subarray
imin = imid + 1;
else
// change max index to search lower subarray
imax = imid - 1;
}
// key was not found
return KEY_NOT_FOUND;
}
source: wikipedia.org

Answer 2

$array = [3, 7, 12, 63, 120, 512, 961];
$min = 0;
$max = count($array)-1;
$no = 320;
while ($min < $max)
{
$mid = (int)(($min+$max)/2);
if ($array[$mid] == $no) {
print $array[$mid-1]."<".$no."<".$array[$mid+1];
return;
}
else if($array[$mid] < $no) {
$min = $mid+1;
} else {
$max = $mid-1;
}
if($min == $max ) {
if($array[$min] > $no) {
print $array[$min-1]."<".$no."<".$array[$min];
return;
} else {
print $array[$min]."<".$no."<".$array[$min+1];
return;
}
}
}