Detecting Duplicate Elements in an Array Using PHP

Introduction

Detecting duplicate elements in an array requires traversing each element and checking whether any value appears more than once, ensuring that no possible duplicate is missed.

Problem Description

Given an integer array nums , return true if any value appears at least twice; otherwise return false when every element is unique.

Example

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

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

Exploring the Code

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 : The function creates an empty associative array $map 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 as a key in $map .

If it exists, a duplicate has been found and the function immediately returns true .

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

3. Return Value : After scanning the entire array without finding duplicates, the function returns false , indicating that the array contains only unique 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 entries in the worst case (when no duplicates exist).

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.