Detecting Duplicate Elements in an Array with PHP

Given an integer array nums , the task is to return true if any value appears at least twice; otherwise return false .

Below is the PHP implementation. The class Solution defines the method containsDuplicate($nums) , which uses an associative array $map to record elements that have been seen.

class Solution {

    /**
     * @param Integer[] $nums
     * @return Boolean
     */
    function containsDuplicate($nums) {
        $map = array();
        foreach ($nums as $n => $i) {
            if (array_key_exists($i, $map)) {
                return true;
            }
            $map[$i] = $n;
        }
        return false;
    }
}

Function execution flow:

Initialize an empty associative array $map to store elements and their indices.

Iterate over each element in $nums .

For each element, check whether it already exists in $map . If it does, a duplicate is found and the function returns true .

If the element is not present, add it to $map with its index for future checks.

After processing the entire array without finding duplicates, return false .

The algorithm runs in O(n) time, where n is the number of elements in the input array, because each element is examined exactly once.

The space complexity is also O(n) , as the associative array may store up to n unique elements in the worst case.

In conclusion, the optimized PHP solution leverages an associative array for constant‑time lookups, enabling fast and reliable detection of duplicate elements while maintaining linear time and space performance.