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Odd-Even Sort / Brick Sort
  • Difficulty Level : Easy
  • Last Updated : 31 Mar, 2021
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This is basically a variation of bubble-sort. This algorithm is divided into two phases- Odd and Even Phase. The algorithm runs until the array elements are sorted and in each iteration two phases occurs- Odd and Even Phases.
In the odd phase, we perform a bubble sort on odd indexed elements and in the even phase, we perform a bubble sort on even indexed elements.
 

C++




// A C++ Program to implement Odd-Even / Brick Sort
#include<bits/stdc++.h>
using namespace std;
 
// A function to sort the algorithm using Odd Even sort
void oddEvenSort(int arr[], int n)
{
    bool isSorted = false; // Initially array is unsorted
 
    while (!isSorted)
    {
        isSorted = true;
 
        // Perform Bubble sort on odd indexed element
        for (int i=1; i<=n-2; i=i+2)
        {
            if (arr[i] > arr[i+1])
             {
                swap(arr[i], arr[i+1]);
                isSorted = false;
              }
        }
 
        // Perform Bubble sort on even indexed element
        for (int i=0; i<=n-2; i=i+2)
        {
            if (arr[i] > arr[i+1])
            {
                swap(arr[i], arr[i+1]);
                isSorted = false;
            }
        }
    }
 
    return;
}
 
// A utility function ot print an array of size n
void printArray(int arr[], int n)
{
   for (int i=0; i < n; i++)
       cout << arr[i] << " ";
   cout << "\n";
}
 
// Driver program to test above functions.
int main()
{
    int arr[] = {34, 2, 10, -9};
    int n = sizeof(arr)/sizeof(arr[0]);
 
    oddEvenSort(arr, n);
    printArray(arr, n);
 
    return (0);
}

Java




// Java Program to implement
// Odd-Even / Brick Sort
import java.io.*;
 
class GFG
{
    public static void oddEvenSort(int arr[], int n)
    {
        boolean isSorted = false; // Initially array is unsorted
 
        while (!isSorted)
        {
            isSorted = true;
            int temp =0;
 
            // Perform Bubble sort on odd indexed element
            for (int i=1; i<=n-2; i=i+2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
 
            // Perform Bubble sort on even indexed element
            for (int i=0; i<=n-2; i=i+2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
        }
 
        return;
    }
    public static void main (String[] args)
    {
        int arr[] = {34, 2, 10, -9};
        int n = arr.length;
 
        oddEvenSort(arr, n);
        for (int i=0; i < n; i++)
            System.out.print(arr[i] + " ");
 
        System.out.println(" ");
    }
}
// Code Contribute by Mohit Gupta_OMG <(0_o)>

Python3




# Python Program to implement
# Odd-Even / Brick Sort
 
def oddEvenSort(arr, n):
    # Initially array is unsorted
    isSorted = 0
    while isSorted == 0:
        isSorted = 1
        temp = 0
        for i in range(1, n-1, 2):
            if arr[i] > arr[i+1]:
                arr[i], arr[i+1] = arr[i+1], arr[i]
                isSorted = 0
                 
        for i in range(0, n-1, 2):
            if arr[i] > arr[i+1]:
                arr[i], arr[i+1] = arr[i+1], arr[i]
                isSorted = 0
     
    return
 
 
arr = [34, 2, 10, -9]
n = len(arr)
 
oddEvenSort(arr, n);
for i in range(0, n):
    print(arr[i], end = ' ')
     
# Code Contribute by Mohit Gupta_OMG <(0_o)>

C#




// C# Program to implement
// Odd-Even / Brick Sort
using System;
 
class GFG
{
    public static void oddEvenSort(int []arr, int n)
    {
        // Initially array is unsorted
        bool isSorted = false;
 
        while (!isSorted)
        {
            isSorted = true;
            int temp =0;
 
            // Perform Bubble sort on
            // odd indexed element
            for (int i = 1; i <= n - 2; i = i + 2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
 
            // Perform Bubble sort on
            // even indexed element
            for (int i = 0; i <= n - 2; i = i + 2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
        }
        return;
    }
     
    // Driver code
    public static void Main ()
    {
        int []arr = {34, 2, 10, -9};
        int n = arr.Length;
         
        // Function calling
        oddEvenSort(arr, n);
        for (int i = 0; i < n; i++)
            Console.Write(arr[i] + " ");
 
        Console.WriteLine(" ");
    }
}
 
// This code is contributed by Sam007

Javascript




<script>
 
// Javascript Program to implement
// Odd-Even / Brick Sort
 
   function oddEvenSort(arr, n)
    {
        // Initially array is unsorted
   
        let isSorted = false;
         
        while (!isSorted)
        {
            isSorted = true;
            let temp =0;
   
            // Perform Bubble sort on odd indexed element
            for (let i=1; i<=n-2; i=i+2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
   
            // Perform Bubble sort on even indexed element
            for (let i=0; i<=n-2; i=i+2)
            {
                if (arr[i] > arr[i+1])
                {
                    temp = arr[i];
                    arr[i] = arr[i+1];
                    arr[i+1] = temp;
                    isSorted = false;
                }
            }
        }
   
        return;
    }
 
// Driver Code
     
        let arr = [34, 2, 10, -9];
        let n = arr.length;
   
        oddEvenSort(arr, n);
        for (let i=0; i < n; i++)
            document.write(arr[i] + " ");
   
        document.write(" ");
         
</script>

Output : 

-9 2 10 34 

We demonstrate the above algorithm using the below illustration on the array = {3, 2, 3, 8, 5, 6, 4, 1}
 

Please refer wiki for proof of correctness.
Time Complexity : O(N2) where, N = Number of elements in the input array.
Auxiliary Space : O(1). Just like bubble sort this is also an in-place algorithm.
Exercise 
In our program in each iteration we first do bubble sort on odd indexed elements and then a bubble sort on the even indexed elements.
Will we get a sorted result if we first perform a bubble sort on even indexed element first and then on the odd indexed element ?
References 
https://en.wikipedia.org/wiki/Odd%E2%80%93even_sort 
This article is contributed by Rachit Belwariar. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
 

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