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Segregate even and odd numbers | Set 3
  • Difficulty Level : Easy
  • Last Updated : 23 Oct, 2018

Given an array of integers, segregate even and odd numbers in the array. All the even numbers should be present first, and then the odd numbers.

Examples:

Input : 1 9 5 3 2 6 7 11
Output : 2 6 5 3 1 9 7 11

Input : 1 3 2 4 7 6 9 10
Output : 2 4 6 10 7 1 9 3

We have discussed two different approaches in below posts:

  1. Segregate Even and Odd numbers
  2. Segregate even and odd numbers | Set 2

The idea discussed in this post is based on Lomuto’s Partition Scheme

  1. Maintain a pointer to the position before first odd element in the array.
  2. Traverse the array and if even number is encountered then swap it with the first odd element.
  3. Continue the traversal.

C++

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// CPP code to segregate even odd
// numbers in an array
#include <bits/stdc++.h>
using namespace std;
  
// Function to segregate even odd numbers
void arrayEvenAndOdd(int arr[], int n)
{
  
    int i = -1, j = 0;
    int t;
    while (j != n) {
        if (arr[j] % 2 == 0) {
            i++;
  
            // Swapping even and odd numbers
            swap(arr[i], arr[j]);
        }
        j++;
    }
  
    // Printing segregated array
    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
}
  
// Driver code
int main()
{
    int arr[] = { 1, 3, 2, 4, 7, 6, 9, 10 };
    int n = sizeof(arr) / sizeof(int);
    arrayEvenAndOdd(arr, n);
    return 0;
}

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Java

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// java code to segregate even odd
// numbers in an array
public class GFG {
       
    // Function to segregate even
    // odd numbers
    static void arrayEvenAndOdd(
                  int arr[], int n)
    {
       
        int i = -1, j = 0;
        while (j != n) {
            if (arr[j] % 2 == 0)
            {
                i++;
       
                // Swapping even and
                // odd numbers
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
            j++;
        }
       
        // Printing segregated array
        for (int k = 0; k < n; k++)
             System.out.print(arr[k] + " ");
    }
     
    // Driver code
    public static void main(String args[])
    {
        int arr[] = { 1, 3, 2, 4, 7
                            6, 9, 10 };
        int n = arr.length;
        arrayEvenAndOdd(arr, n);
    }
}
  
// This code is contributed by Sam007

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Python3

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# Python3 code to segregate even odd 
# numbers in an array 
  
# Function to segregate even odd numbers 
def arrayEvenAndOdd(arr,n):
    i = -1
    j= 0
    while (j!=n):
        if (arr[j] % 2 ==0):
            i = i+1
  
            # Swapping even and odd numbers 
            arr[i],arr[j] = arr[j],arr[i]
              
        j = j+1
      
    # Printing segregated array 
    for i in arr:
        print (str(i) + " " ,end='')
          
# Driver Code
if __name__=='__main__':
    arr = [ 1 ,3, 2, 4, 7, 6, 9, 10]
    n = len(arr)
    arrayEvenAndOdd(arr,n)
  
# This code was contributed by 
# Yatin Gupta

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C#

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// C# code to segregate even odd
// numbers in an array
using System;
  
class GFG {
      
    // Function to segregate even
    // odd numbers
    static void arrayEvenAndOdd(
                  int []arr, int n)
    {
      
        int i = -1, j = 0;
        while (j != n) {
            if (arr[j] % 2 == 0)
            {
                i++;
      
                // Swapping even and
                // odd numbers
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
            j++;
        }
      
        // Printing segregated array
        for (int k = 0; k < n; k++)
            Console.Write(arr[k] + " ");
    }
  
    // Driver code    
    static void Main()
    {
        int []arr = { 1, 3, 2, 4, 7, 
                            6, 9, 10 };
        int n = arr.Length;
        arrayEvenAndOdd(arr, n);
    }
}
  
// This code is contributed by Sam007

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PHP

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<?php
// PHP code to segregate even odd
// numbers in an array
  
// Function to segregate
// even odd numbers
function arrayEvenAndOdd($arr, $n)
{
    $i = -1;
    $j = 0;
    $t;
    while ($j != $n)
    {
        if ($arr[$j] % 2 == 0)
        {
            $i++;
  
            // Swapping even and
            // odd numbers
            $x = $arr[$i];
            $arr[$i] = $arr[$j];
            $arr[$j] = $x;
        }
        $j++;
    }
  
    // Printing segregated 
    // array
    for ($i = 0; $i < $n; $i++)
        echo $arr[$i] . " ";
}
  
    // Driver code
    $arr = array(1, 3, 2, 4, 7, 6, 9, 10);
    $n = sizeof($arr);
    arrayEvenAndOdd($arr, $n);
  
// This code is contributed by Anuj_67
?>

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Output:

2 4 6 10 7 1 9 3

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

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