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Php Program for Range Queries for Frequencies of array elements

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  • Last Updated : 06 Jan, 2022

Given an array of n non-negative integers. The task is to find frequency of a particular element in the arbitrary range of array[]. The range is given as positions (not 0 based indexes) in array. There can be multiple queries of given type. 
Examples: 
 

Input  : arr[] = {2, 8, 6, 9, 8, 6, 8, 2, 11};
         left = 2, right = 8, element = 8
         left = 2, right = 5, element = 6      
Output : 3
         1
The element 8 appears 3 times in arr[left-1..right-1]
The element 6 appears 1 time in arr[left-1..right-1]

Naive approach: is to traverse from left to right and update count variable whenever we find the element. 
Below is the code of Naive approach:- 
 

PHP




<?php
// PHP program to find total count of 
// an element in a range
  
// Returns count of element in 
// arr[left-1..right-1]
function findFrequency(&$arr, $n, $left,
                        $right, $element)
{
    $count = 0;
    for ($i = $left - 1; $i <= $right; ++$i)
        if ($arr[$i] == $element)
            ++$count;
    return $count;
}
  
// Driver Code
$arr = array(2, 8, 6, 9, 8, 6, 8, 2, 11);
$n = sizeof($arr);
  
// Print frequency of 2 from position 1 to 6
echo "Frequency of 2 from 1 to 6 = "
      findFrequency($arr, $n, 1, 6, 2) ."
";
  
// Print frequency of 8 from position 4 to 9
echo "Frequency of 8 from 4 to 9 = "
      findFrequency($arr, $n, 4, 9, 8);
  
// This code is contributed by ita_c
?>

Output: 

 Frequency of 2 from 1 to 6 = 1
 Frequency of 8 from 4 to 9 = 2

Time complexity of this approach is O(right – left + 1) or O(n) 
Auxiliary space: O(1)
Please refer complete article on Range Queries for Frequencies of array elements for more details!

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