Detecting Duplicate Elements in an Array with PHP

Detecting duplicate elements in an array requires traversing each element and checking whether it appears more than once, ensuring no duplicates are missed.

Introduction

Given an integer array nums , the function should return true if any value appears at least twice, otherwise false .

Example

Input: nums = [1,2,3,1]
Output: true

Input: nums = [1,2,3,4]
Output: false

Exploring the Code

We examine the PHP class Solution and its method containsDuplicate($nums) :

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

1. Initialization: An empty associative array $map is created to store elements and their indices.

2. Duplicate Detection:

The function iterates over each element in $nums .

For each element, it checks whether the element already exists in $map .

If it exists, the function immediately returns true , indicating a duplicate.

If not, the element and its index are added to $map for future checks.

3. Return Value: If the loop finishes without finding duplicates, the function returns false , meaning all elements are unique.

Time and Space Complexity

Time complexity: O(n) , where n is the number of elements in the input array, because each element is examined once.

Space complexity: O(n) , as the associative array $map may store up to n entries in the worst case (no duplicates).

Conclusion

The optimized PHP solution uses an associative array for constant‑time lookups, enabling fast and reliable detection of duplicate elements while maintaining linear time and space efficiency.