Why intdiv or >> 1 and not ($lo + $hi) / 2?

The / operator returns a float when the division is not exact, so (0 + 5) / 2 is 2.5. Using a float as an array key truncates it (with a deprecation notice since PHP 8.1), and returning a float from a method declared : int relies on the same lossy coercion. intdiv($lo + $hi, 2) or ($lo + $hi) >> 1 keep the midpoint an integer.

Does PHP have a built-in binary search?

No. array_search and in_array scan the array linearly, so they are the O(n) approach in one call. A short lowerBound helper like the one in the second approach is the usual way to get O(log n).

Why not array_search($target, $nums)?

array_search returns the key of the first match or false when there is none, so you would write $i = array_search($target, $nums, true); return $i === false ? -1 : $i;. It passes, but it is a linear scan, and without the third true argument it compares loosely.

Can $lo + $hi overflow in PHP?

PHP integers are 64-bit on every current build, and an array of 5,000 elements keeps the indices tiny, so no. If an integer did overflow, PHP would silently turn it into a float rather than wrap.

Are the keys of $nums always 0 to n - 1?

For the arrays the runner passes, yes: they are lists, so $nums[$mid] and count($nums) - 1 line up with positions. An array built with unset or string keys would not be a list, and you would call array_values($nums) first.

Search in Rotated Sorted Array in PHP: Scan and Binary Search Solutions

search.php

PHP 8.5

Not run yet

+ 8 hidden

Input

nums = [15, 22, 30, 4, 9, 11]
target = 9

Expected

This is [4, 9, 11, 15, 22, 30] rotated so it starts at 15. The 9 sits at index 4.