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Segregate even and odd numbers | Set 2
  • Difficulty Level : Easy
  • Last Updated : 03 May, 2021

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 : 6 2 3 5 2 9 11 1

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

 

We have discussed one approach in Segregate Even and Odd numbers. In this post, a different simpler approach is discussed that uses an extra array.
Approach : 
1. Start two pointers from left and right of the array. 
2. Create a new array of same size as given. 
3. If the element at left or right is even then put it in front of the array else at the end.
 

C++




// 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 b[n];  // To store result
  int k = 0, l = n - 1, i, j;
  for (i = 0, j = n - 1; i < j; i++, j--) {
 
    if (arr[i] % 2 == 0) {
      b[k] = arr[i];
      k++;
    } else {
      b[l] = arr[i];
      l--;
    }
 
    if (arr[j] % 2 == 0) {
      b[k] = arr[j];
      k++;
    } else {
      b[l] = arr[j];
      l--;
    }
  }
 
  // for i == j in case of odd length
  b[i] = arr[i];
 
  // Printing segregated array
  for (int i = 0; i < n; i++)
     cout << b[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;
}

Java




// Java code to segregate even odd
// numbers in an array
import java.util.Arrays;
 
class arr
{
    // Function to segregate even odd numbers
    static void arrayEvenAndOdd(int arr[], int n)
    {
        // To store result
        int b[] = new int[n];
        int k = 0, l = n - 1, i, j;
        for (i = 0, j = n - 1; i < j; i++, j--)
        {
         
            if (arr[i] % 2 == 0)
            {
                b[k] = arr[i];
                k++;
            }
            else
            {
                b[l] = arr[i];
                l--;
            }
         
            if (arr[j] % 2 == 0)
            {
                b[k] = arr[j];
                k++;
            }
            else
            {
                b[l] = arr[j];
                l--;
            }
        }
     
        // for i == j in case of odd length
        b[i] = arr[i];
         
        // Printing segregated array
        for (i = 0; i < n; i++)
        {
            System.out.print(b[i] + " ");
        }
    }
     
    // 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 Smitha Dinesh Semwal

Python3




# Python3 code to segregate even odd
# numbers in an array
 
# Function to segregate even odd numbers
def arrayEvenAndOdd(arr,n): 
 
    b = [0] * # To store result
    k = 0
    l = n - 1
    i = 0
    j = n-1
    while(i < j):
        if (arr[i] % 2 == 0): 
            b[k] = arr[i]
            k+=1
        else
            b[l] = arr[i]
            l-=1
        if (arr[j] % 2 == 0): 
            b[k] = arr[j]
            k+=1
        else
            b[l] = arr[j]
            l-=1
        i+=1
        j-=1
      
  
 
    # for i == j in case of odd length
    b[i] = arr[i]
 
    # Printing segregated array
    for i in range(0, n):
        print(b[i],end=" "
  
 
# Driver code
arr =  [1, 3, 2, 4, 7, 6, 9, 10
n = len(arr)
 
arrayEvenAndOdd(arr, n)
 
# This code is contributed by
# Smitha Dinesh Semwal

C#




// 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)
    {
         
        // To store result
        int []b = new int[n];
        int k = 0, l = n - 1, i, j;
        for (i = 0, j = n - 1; i < j; i++, j--)
        {
         
            if (arr[i] % 2 == 0)
            {
                b[k] = arr[i];
                k++;
            }
            else
            {
                b[l] = arr[i];
                l--;
            }
         
            if (arr[j] % 2 == 0)
            {
                b[k] = arr[j];
                k++;
            }
            else
            {
                b[l] = arr[j];
                l--;
            }
        }
     
        // for i == j in case of odd length
        b[i] = arr[i];
         
        // Printing segregated array
        for (i = 0; i < n; i++)
        {
            Console.Write(b[i] + " ");
        }
    }
     
    // Driver code
    public 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 vt_m.

Javascript




<script>
// Java  scriptcode to segregate even odd
// numbers in an array
 
 
    // Function to segregate even odd numbers
    function arrayEvenAndOdd(arr,n)
    {
        // To store result
        let b=[n];
        let k = 0, l = n - 1, i, j;
        for (i = 0, j = n - 1; i < j; i++, j--)
        {
         
            if (arr[i] % 2 == 0)
            {
                b[k] = arr[i];
                k++;
            }
            else
            {
                b[l] = arr[i];
                l--;
            }
         
            if (arr[j] % 2 == 0)
            {
                b[k] = arr[j];
                k++;
            }
            else
            {
                b[l] = arr[j];
                l--;
            }
        }
     
        // for i == j in case of odd length
        b[i] = arr[i];
         
        // Printing segregated array
        for (i = 0; i < n; i++)
        {
            document.write(b[i] + " ");
        }
    }
     
    // Driver code
     
        let arr = [1, 3, 2, 4, 7, 6, 9, 10];
        let n = arr.length;
        arrayEvenAndOdd(arr, n);
 
 
// This code is contributed by sravan kumar Gottumukkala
</script>
Output: 
10 2 6 4 7 9 3 1

 

Time Complexity : O(n/2) 
Auxiliary Space : O(n)
 




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