# Rearrange array such that arr[i] >= arr[j] if i is even and arr[i]<=arr[j] if i is odd and j < i

Given an array of n elements. Our task is to write a program to rearrange the array such that elements at even positions are greater than all elements before it and elements at odd positions are less than all elements before it.

Examples:

Input : arr[] = {1, 2, 3, 4, 5, 6, 7}
Output : 4 5 3 6 2 7 1

Input : arr[] = {1, 2, 1, 4, 5, 6, 8, 8}
Output : 4 5 2 6 1 8 1 8

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

The idea to solve this problem is to first create an auxiliary copy of the original array and sort the copied array. Now total number of even position in array with n elements will be floor(n/2) and remaining is the number of odd positions. Now fill the odd and even positions in the original array using the sorted array in the below manner:

• Total odd positions will be n – floor(n/2). Start from (n-floor(n/2))th position in the sorted array and copy the element to 1st position of sorted array. Start traversing the sorted array from this position towards left and keep filling the odd positions in the original array towrds right.
• Start traversing the sorted array starting from (n-floor(n/2)+1)th position towards right and keep filling the original array starting from 2nd position.

Below is the implementation of above idea:

## C++

 // C++ program to rearrange the array // as per the given condition    #include using namespace std;    // function to rearrange the array void rearrangeArr(int arr[], int n) {     // total even positions     int evenPos = n / 2;        // total odd positions     int oddPos = n - evenPos;        int tempArr[n];        // copy original array in an     // auxiliary array     for (int i = 0; i < n; i++)         tempArr[i] = arr[i];        // sort the auxiliary array     sort(tempArr, tempArr + n);        int j = oddPos - 1;        // fill up odd position in original     // array     for (int i = 0; i < n; i += 2) {         arr[i] = tempArr[j];         j--;     }        j = oddPos;        // fill up even positions in original     // array     for (int i = 1; i < n; i += 2) {         arr[i] = tempArr[j];         j++;     }        // display array     for (int i = 0; i < n; i++)         cout << arr[i] << " "; }    // Driver code int main() {     int arr[] = { 1, 2, 3, 4, 5, 6, 7 };     int size = sizeof(arr) / sizeof(arr[0]);     rearrangeArr(arr, size);     return 0; }

## Java

 // Java program to rearrange the array // as per the given condition import java.util.*; import java.lang.*;    public class GfG{     // function to rearrange the array     public static void rearrangeArr(int arr[],                                         int n)     {         // total even positions         int evenPos = n / 2;            // total odd positions         int oddPos = n - evenPos;            int[] tempArr = new int [n];            // copy original array in an         // auxiliary array         for (int i = 0; i < n; i++)             tempArr[i] = arr[i];            // sort the auxiliary array         Arrays.sort(tempArr);            int j = oddPos - 1;            // fill up odd position in          // original array         for (int i = 0; i < n; i += 2) {             arr[i] = tempArr[j];             j--;         }            j = oddPos;            // fill up even positions in          // original array         for (int i = 1; i < n; i += 2) {             arr[i] = tempArr[j];             j++;         }            // display array         for (int i = 0; i < n; i++)             System.out.print(arr[i] + " ");     }            // Driver function      public static void main(String argc[]){         int[] arr = new int []{ 1, 2, 3, 4, 5,                                         6, 7 };         int size = 7;         rearrangeArr(arr, size);                } }    /* This code is contributed by Sagar Shukla */

## Python3

 # Python3 code to rearrange the array # as per the given condition import array as a import numpy as np    # function to rearrange the array def rearrangeArr(arr, n):            # total even positions     evenPos = int(n / 2)        # total odd positions     oddPos = n - evenPos        # intialising empty array in python     tempArr = np.empty(n, dtype = object)        # copy original array in an     # auxiliary array     for i in range(0, n):                    tempArr[i] = arr[i]        # sort the auxiliary array     tempArr.sort()        j = oddPos - 1        # fill up odd position in original     # array     for i in range(0, n, 2):            arr[i] = tempArr[j]         j = j - 1            j = oddPos        # fill up even positions in original     # array     for i in range(1, n, 2):         arr[i] = tempArr[j]         j = j + 1            # display array     for i in range(0, n):         print (arr[i], end = ' ')    # Driver code arr = a.array('i', [ 1, 2, 3, 4, 5, 6, 7 ]) rearrangeArr(arr, 7)    # This code is contributed by saloni1297

## C#

 // C# program to rearrange the array // as per the given condition using System;    public class GfG {            // Function to rearrange the array     public static void rearrangeArr(int []arr, int n)     {         // total even positions         int evenPos = n / 2;            // total odd positions         int oddPos = n - evenPos;            int[] tempArr = new int [n];            // copy original array in an         // auxiliary array         for (int i = 0; i < n; i++)             tempArr[i] = arr[i];            // sort the auxiliary array         Array.Sort(tempArr);            int j = oddPos - 1;            // Fill up odd position in          // original array         for (int i = 0; i < n; i += 2) {             arr[i] = tempArr[j];             j--;         }            j = oddPos;            // Fill up even positions in          // original array         for (int i = 1; i < n; i += 2) {             arr[i] = tempArr[j];             j++;         }            // display array         for (int i = 0; i < n; i++)             Console.Write(arr[i] + " ");     }            // Driver Code      public static void Main()     {         int[] arr = new int []{ 1, 2, 3, 4, 5, 6, 7 };         int size = 7;         rearrangeArr(arr, size);     } }    /* This code is contributed by vt_m */

## PHP



Output:

4 5 3 6 2 7 1

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

## tags:

Arrays array-rearrange Sorting Quiz Arrays