219. Contains Duplicate II

class Solution {

    /**
     * @param Integer[] $nums
     * @param Integer $k
     * @return Boolean
     */
    function containsNearbyDuplicate($nums, $k) {
        $compares = [];
        foreach($nums as $index => $num){
            if (isset($compares[$num]) && abs($compares[$num] - $index) <= $k) {
                return true;    
            }
            
            $compares[$num] = $index;
        }

        return false;
    }
}