PHP Program to Find the Number Occurring Odd Number of Times

Last Updated : 24 Oct, 2023

Write a PHP program for a given array of positive integers. All numbers occur an even number of times except one number which occurs an 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 Program to Find the Number Occurring Odd Number of Times using Nested Loop:

A Simple Solution is to run two nested loops. The outer loop picks all elements one by one and the inner loop counts the number of occurrences of the element picked by the outer loop.

Below is the implementation of the brute force approach :

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

Time Complexity: O(n^2)
Auxiliary Space: O(1)

PHP Program to Find the Number Occurring Odd Number of Times using Hashing:

A Better Solution is to use Hashing. Use array elements as a key and their counts as values. Create an empty hash table. One by one traverse the given array elements and store counts.

Below is the implementation of the above approach:

PHP

<?php

function getOddOccurrence($arr, $size) {
    $hash = [];

    // Putting all elements into the HashMap
    for ($i = 0; $i < $size; $i++) {
        $element = $arr[$i];
        if (isset($hash[$element])) {
            $hash[$element]++;
        } else {
            $hash[$element] = 1;
        }
    }

    // Iterate through the HashMap to check an element
    // occurring an odd number of times and return it
    foreach ($hash as $element => $count) {
        if ($count % 2 != 0) {
            return $element;
        }
    }
    return -1;
}

$arr = [2, 3, 5, 4, 5, 2, 4, 3, 5, 2, 4, 4, 2];
$n = count($arr);

// Function calling
echo getOddOccurrence($arr, $n);

?>

Output

Time Complexity: O(n)
Auxiliary Space: O(n)

PHP Program to Find the Number Occurring Odd Number of Times using Bit Manipulation:

The Best Solution is to do bitwise XOR of all the elements. XOR of all elements gives us odd occurring elements.

Here ^ is the XOR operators;
Note :
x^0 = x
x^y=y^x (Commutative property holds)
(x^y)^z = x^(y^z) (Distributive property holds)
x^x=0

Below is the implementation of the above approach.

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
?>

Output

Time Complexity: O(n)
Auxiliary Space: O(1)

Please refer complete article on Find the Number Occurring Odd Number of Times for more details!

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Article Tags :

PHP Program to Find the Number Occurring Odd Number of Times

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

PHP Program to Find the Number Occurring Odd Number of Times using Nested Loop:

PHP Program to Find the Number Occurring Odd Number of Times using Hashing:

PHP Program to Find the Number Occurring Odd Number of Times using Bit Manipulation:

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