Rearrange an array in order – smallest, largest, 2nd smallest, 2nd largest, ..

Given an array of integers, the task is to print the array in the order – smallest number, the Largest number, 2nd smallest number, 2nd largest number, 3rd smallest number, 3rd largest number, and so on…..

Examples:

Input : arr[] = [5, 8, 1, 4, 2, 9, 3, 7, 6]
Output :arr[] = {1, 9, 2, 8, 3, 7, 4, 6, 5}

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

A simple solution is to first find the smallest element and swap it with the first element. Then find the largest element, swap it with the second element, and so on. The time complexity of this solution is O(n²).

An efficient solution is to use sorting. 

1. Sort the elements of the array. 
2. Take two variables say i and j and point them to the first and last index of the array respectively. 
3. Now run a loop and store the elements in the array one by one by incrementing i and decrementing j.

Let’s take an array with input 5, 8, 1, 4, 2, 9, 3, 7, 6 and sort them so the array becomes 1, 2, 3, 4, 5, 6, 7, 8, 9. Now take two variables to say i and j and point them to the first and last index of the array respectively, run a loop, and store the value into a new array by incrementing I and decrementing j.get that the final result as 1 9 2 8 3 7 4 6 5. 

The flowchart is as follows:

flowchart- rearrangearray

Implementation:

C++

// C++ program to print the array in given order
#include <bits/stdc++.h>
using namespace std;

// Function which arrange the array.
void rearrangeArray(int arr[], int n)
{
    // Sorting the array elements
    sort(arr, arr + n);

    int tempArr[n]; // To store modified array

    // Adding numbers from sorted array to
    // new array accordingly
    int ArrIndex = 0;

    // Traverse from begin and end simultaneously
    for (int i = 0, j = n - 1; i <= n / 2 || j > n / 2;
         i++, j--) {
        tempArr[ArrIndex] = arr[i];
        ArrIndex++;
        tempArr[ArrIndex] = arr[j];
        ArrIndex++;
    }

    // Modifying original array
    for (int i = 0; i < n; i++)
        arr[i] = tempArr[i];
}

// Driver Code
int main()
{
    int arr[] = { 5, 8, 1, 4, 2, 9, 3, 7, 6 };
    int n = sizeof(arr) / sizeof(arr[0]);
    rearrangeArray(arr, n);

    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";

    return 0;
}

Java

// Java program to print the array in given order
import java.util.Arrays;

public class GFG {

    // Function which arrange the array.
    static void rearrangeArray(int arr[], int n)
    {
        // Sorting the array elements
        Arrays.sort(arr);

        int[] tempArr = new int[n]; // To store modified array

        // Adding numbers from sorted array to
        // new array accordingly
        int ArrIndex = 0;

        // Traverse from begin and end simultaneously
        for (int i = 0, j = n-1; i <= n / 2 || j > n / 2;
                                           i++, j--) {
            if(ArrIndex < n)
            {
                tempArr[ArrIndex] = arr[i];
                ArrIndex++;
            }

            if(ArrIndex < n)
            {
                tempArr[ArrIndex] = arr[j];
                ArrIndex++;
            }
        }

        // Modifying original array
        for (int i = 0; i < n; i++)
            arr[i] = tempArr[i];
    }

    // Driver Code
    public static void main(String args[])
    {
        int arr[] = { 5, 8, 1, 4, 2, 9, 3, 7, 6 };
        int n = arr.length;
        rearrangeArray(arr, n);

        for (int i = 0; i < n; i++)
            System.out.print(arr[i]+" ");
    }
}
// This code is contributed by Sumit Ghosh

Python3

# Python 3 program to print
# the array in given order

# Function which arrange the
# array.
def rearrangeArray(arr, n) :

    # Sorting the array elements
    arr.sort()

    # To store modified array
    tempArr = [0] * (n + 1)

    # Adding numbers from sorted
    # array to new array accordingly
    ArrIndex = 0

    # Traverse from begin and end
    # simultaneously
    i = 0
    j = n-1

    while(i <= n // 2 or j > n // 2 ) :

        tempArr[ArrIndex] = arr[i]
        ArrIndex = ArrIndex + 1
        tempArr[ArrIndex] = arr[j]
        ArrIndex = ArrIndex + 1
        i = i + 1
        j = j - 1

    # Modifying original array
    for i in range(0, n) :
        arr[i] = tempArr[i]


# Driver Code
arr = [ 5, 8, 1, 4, 2, 9, 3, 7, 6 ]
n = len(arr)
rearrangeArray(arr, n)

for i in range(0, n) :
    print( arr[i], end = " ")

# This code is contributed by Nikita Tiwari.

C#

// C# program to print the
// array in given order
using System;

public class GFG {

    // Function which arrange the array.
    static void rearrangeArray(int []arr, int n)
    {
        // Sorting the array elements
        Array.Sort(arr);

        // To store modified array
        int []tempArr = new int[n];

        // Adding numbers from sorted array
        // to new array accordingly
        int ArrIndex = 0;

        // Traverse from begin and end simultaneously
        for (int i = 0, j = n-1; i <= n / 2
             || j > n / 2; i++, j--) {

            if(ArrIndex < n)
            {
                tempArr[ArrIndex] = arr[i];
                ArrIndex++;
            }

            if(ArrIndex < n)
            {
                tempArr[ArrIndex] = arr[j];
                ArrIndex++;
            }
        }

        // Modifying original array
        for (int i = 0; i < n; i++)
            arr[i] = tempArr[i];
    }

    // Driver Code
    public static void Main(String []args)
    {
        int []arr = {5, 8, 1, 4, 2, 9, 3, 7, 6};
        int n = arr.Length;
        rearrangeArray(arr, n);

        for (int i = 0; i < n; i++)
        Console.Write(arr[i] + " ");
    }
}

// This code is contributed by Nitin Mittal.

PHP

<?php
// PHP program to print
// the array in given order

// Function which
// arrange the array.
function rearrangeArray($arr, $n)
{
    // Sorting the
    // array elements
    sort($arr);

    // To store modified array
    $tempArr = array($n);

    // Adding numbers from
    // sorted array to new
    // array accordingly
    $ArrIndex = 0;

    // Traverse from begin
    // and end simultaneously
    for ($i = 0, $j = $n - 1;
         $i <= $n / 2 || $j > $n / 2;
         $i++, $j--)
    {
        $tempArr[$ArrIndex] = $arr[$i];
        $ArrIndex++;
        $tempArr[$ArrIndex] = $arr[$j];
        $ArrIndex++;
    }

    // Modifying original array
    for ($i = 0; $i < $n; $i++)
        $arr[$i] = $tempArr[$i];

    for ($i = 0; $i < $n; $i++)
        echo $arr[$i] . " ";
}

// Driver Code
$arr = array(5, 8, 1, 4, 2,
             9, 3, 7, 6 );
$n = count($arr) ;
rearrangeArray($arr, $n);

// This code is contributed
// by Sam007
?>

Javascript

<script>

// Javascript program to print the
// array in given order

// Function which arrange the array.
function rearrangeArray(arr, n)
{
    // Sorting the array elements
    arr.sort();

    // To store modified array
    let tempArr = new Array(n);

    // Adding numbers from sorted array
    // to new array accordingly
    let ArrIndex = 0;

    // Traverse from begin and end simultaneously
    for (let i = 0, j = n-1; i <= n / 2
         || j > n / 2; i++, j--) {

        if(ArrIndex < n)
        {
            tempArr[ArrIndex] = arr[i];
            ArrIndex++;
        }

        if(ArrIndex < n)
        {
            tempArr[ArrIndex] = arr[j];
            ArrIndex++;
        }
    }

    // Modifying original array
    for (let i = 0; i < n; i++)
        arr[i] = tempArr[i];
}

// Driver Code

let arr =[5, 8, 1, 4, 2, 9, 3, 7, 6]
let n = arr.length;
rearrangeArray(arr, n);

for (let i = 0; i < n; i++)
    document.write(arr[i] + " ");


</script>

Output

1 9 2 8 3 7 4 6 5 

Time Complexity: O(n log n), 

Auxiliary Space: O(n), since n extra space has been taken.

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