Find Maximum Value of an Array in PHP
What you’ll learn
- The classic linear scan: keep a running maximum and update it whenever you see a larger element.
- A reusable
findMaxfunction,count($array)for size, and clean PHP output withecho. - A second example with all negative values, plus a live preview for the reference array.
Overview
You walk the array once. The answer after visiting every slot is the largest value stored—no sorting required.
Two programs
Reference mix of positives and an all-negative demo.
Live preview
Same six numbers as example 1; prints the max in the page.
Interview hook
Mention O(n) time and the empty-array edge case when asked.
Prerequisites
for/foreach loops, arrays, and echo.
- Basic PHP syntax and indexed arrays like
$arr = [ ... ]. - Understanding
count($arr)to get array length.
The idea
Pick the first element as your provisional winner. For each next element, if it is greater than the current winner, replace the winner. After the last index, the winner is the maximum.
This is one pass, left to right—easy to code and easy to explain in an interview.
Live preview
Uses the same six integers as example 1: 14, 7, 25, 31, 10, 42.
Algorithm
Goal: return the largest value among n integers in contiguous memory.
Validate length
Require size >= 1 (or handle empty arrays explicitly in production code).
Initialize
Set max = arr[0].
Scan
For i from 1 to size - 1, if arr[i] > max, set max = arr[i].
Return
Return max.
📜 Pseudocode
function findMax(arr): // assume length >= 1
max ← arr[0]
for i from 1 to length(arr) - 1:
if arr[i] > max:
max ← arr[i]
return maxFind maximum (reference program)
Matches the reference behavior: reusable findMax function with a sample array and single-pass scan.
<?php
function findMax(array $arr): int
{
$maxVal = $arr[0];
for ($i = 1; $i < count($arr); $i++) {
if ($arr[$i] > $maxVal) {
$maxVal = $arr[$i];
}
}
return $maxVal;
}
$array = [14, 7, 25, 31, 10, 42];
$maxValue = findMax($array);
echo "Maximum value in the array: $maxValue\n";
?>Explanation
Start from the first element, then compare each next value once. This is a true linear scan, so it is simple and efficient for interview use.
When every element is negative
The same function still works: the “maximum” is the least negative value (here −1).
<?php
function findMax(array $arr): int
{
$maxVal = $arr[0];
foreach ($arr as $value) {
if ($value > $maxVal) {
$maxVal = $value;
}
}
return $maxVal;
}
$negatives = [-9, -3, -1, -7];
echo "Maximum (least negative): " . findMax($negatives) . "\n";
?>Notes
Parallel systems. You can split the array and take the max of partial maxima, then combine—useful for very large data in other environments.
Floating-point. Same structure with double; avoid strict equality when comparing floats for “maximum†in numerical code.
❓ FAQ
🔄 Input / output
Programs embed literals. To read user input in PHP CLI, parse a line with trim(fgets(STDIN)), split numbers, cast to integers, then pass the array to findMax.
Edge cases
size == 0
No maximum exists; guard before reading arr[0].
size == 1
The loop body never runs; max_val stays correct as that single element.
⏱️ Time and space complexity
| Approach | Time | Extra space |
|---|---|---|
| Single scan | O(n) | O(1) |
Summary
- Algorithm: running maximum from left to right.
- Cost:
O(n)time,O(1)extra space. - Edge: define behavior when
n = 0.
Finding the maximum in an unsorted array needs at least n − 1 comparisons in the worst case (standard adversary argument). A single left-to-right scan achieves O(n) time and O(1) extra space.
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