PHP Program to Find the Number Occurring Odd Number of Times

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Given an array of positive integers. All numbers occur even number of times except one number which occurs odd number of times. Find the number in O(n) time & constant space.

Examples :

Input : arr = {1, 2, 3, 2, 3, 1, 3}
Output : 3

Input : arr = {5, 7, 2, 7, 5, 2, 5}
Output : 5

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

PHP

<?php 
// PHP program to find the  
// element occurring odd 
// number of times 
  
// Function to find the element  
// occurring odd number of times 
function getOddOccurrence(&$arr, $arr_size) 
{ 
    $count = 0; 
    for ($i = 0;  
         $i < $arr_size; $i++)  
    { 
          
        for ($j = 0; 
             $j < $arr_size; $j++) 
        { 
            if ($arr[$i] == $arr[$j]) 
                $count++; 
        } 
        if ($count % 2 != 0) 
            return $arr[$i]; 
    } 
    return -1; 
} 
  
// Driver code 
$arr = array(2, 3, 5, 4, 5, 2,  
             4, 3, 5, 2, 4, 4, 2); 
$n = sizeof($arr); 
  
// Function calling 
echo(getOddOccurrence($arr, $n)); 
  
// This code is contributed 
// by Shivi_Aggarwal 
?> 

Output:

A Better Solution is to use Hashing. Use array elements as key and their counts as value. Create an empty hash table. One by one traverse the given array elements and store counts. Time complexity of this solution is O(n). But it requires extra space for hashing.

Program :

PHP

<?php 
// PHP program to find the  
// element occurring odd  
// number of times 
  
// Function to find element  
// occurring odd number of times 
function getOddOccurrence(&$ar, $ar_size) 
{ 
    $res = 0;  
    for ($i = 0; $i < $ar_size; $i++)      
        $res = $res ^ $ar[$i]; 
      
    return $res; 
} 
  
// Driver Code 
$ar = array(2, 3, 5, 4, 5, 2, 
            4, 3, 5, 2, 4, 4, 2); 
$n = sizeof($ar); 
  
// Function calling 
echo(getOddOccurrence($ar, $n)); 
      
// This code is contributed  
// by Shivi_Aggarwal 
?> 