PHP code for finding distinct elements common to all rows of a matrix in O(n) time complexity

<?php

class Matrix{
/**
•@param 2D array $matrix
•
•Prints distinct elements common to all rows of the matrix */

        public static function getDistinctElementsCommonToAllRows($matrix){
                // A hash map to store count of elements 
                $hashmap = array();
                $selectedHash = array();
                $rows = count($matrix);
                $cols = count($matrix[0]);
                
                
                for ($i = 0; $i < $rows; $i++) { 
                        // Increment the count of first 
                        // element of the row
                        if(array_key_exists($matrix[$i][0],$hashmap)){        
                                $hashmap[$matrix[$i][0]] = $i+1; 
                        }

                        // Starting from the second element 
                        // of the current row 
                        for ($j = 1; $j < $cols; $j++) {         
                                // If current element is different from 
                                // the previous element i.e. it is appearing 
                                // for the first time in the current row
                                
                                if(array_key_exists($matrix[$i][$j],$hashmap)){
                                        if ($matrix[$i][$j] !== $matrix[$i][$j - 1]){        
                                                $hashmap[$matrix[$i][$j]] = $i+1;
                                        }
                                }else{                                
                                        if ($matrix[$i][$j] !== $matrix[$i][$j - 1]){        
                                                $hashmap[$matrix[$i][$j]] = $i;
                                        }
                                }        
                        }                
                }
                 
                foreach($hashmap as $key => $val){
                        if($val == $rows){
                                $selectedHash[] = $key;
                        }
                }
                return $selectedHash;
        }
}

$mat1 = [[2, 1, 4, 3],[1, 2, 3, 2],[3, 6, 2, 3],[5, 2, 5, 3]];

$mat2 = [[12, 1, 14, 3, 16],[14, 2, 1, 3, 35],[14, 1, 14, 3, 11],[14, 25, 3, 2, 1],[1, 18, 3, 21, 14]];


print_r (Matrix::getDistinctElementsCommonToAllRows($mat1));
Print_r('<br>');
print_r (Matrix::getDistinctElementsCommonToAllRows($mat2));