Detecting Duplicate Elements in an Array Using PHP

Detecting duplicate elements in an array requires traversing each element and checking for multiple occurrences to ensure no duplicates are missed.

Introduction

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

Example:

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

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

Explore Code

Below is the PHP class Solution with the method containsDuplicate($nums) implementing the detection:

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: after completing the traversal without finding duplicates, the function returns false , indicating no duplicate elements.

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 unique elements in the worst case.

Conclusion

The optimized PHP solution uses an associative array for constant‑time lookups, enabling fast and accurate detection of duplicate elements while maintaining stable performance and reliability.