/*
Demonstration of traversing an array from both ends at the same time
in idiomatic PHP.
We use the classic "two‑index" technique:
- $left starts at index 0
- $right starts at index count($array) - 1
Both move toward the center.
This approach is efficient (O(n)), simple, and widely used in
algorithms such as palindrome checks, partitioning, and pair searching.
*/
/* ------------------------------------------------------------
Function: traverseFromBothSides
Purpose: Traverse an array from both ends simultaneously.
------------------------------------------------------------ */
function traverseFromBothSides(array $arr): void
{
$left = 0;
$right = count($arr) - 1;
// Move inward until the indices cross
while ($left <= $right) {
echo "Left: {$arr[$left]}, Right: {$arr[$right]}\n";
$left++;
$right--;
}
}
/* ------------------------------------------------------------
Main program
------------------------------------------------------------ */
$array = [10, 20, 30, 40, 50, 60, 70, 80, 90];
echo "Traversing from both sides:\n";
traverseFromBothSides($array);
/*
run:
Traversing from both sides:
Left: 10, Right: 90
Left: 20, Right: 80
Left: 30, Right: 70
Left: 40, Right: 60
Left: 50, Right: 50
*/
