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

Given an array of integers, task is to print the array in the order – smallest number, 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, swap it with first element. Then find largest element, swap it with second element and so on. Time complexity of this solution is O(n2).

An efficient solution is to use sorting.
1. Sort the elements of 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 become 1, 2, 3, 4, 5, 6, 7, 8, 9. Now take two variables say i and j and point them to the first and last index of the array respectively, run a loop and store value into new array by incrementing i and decrementing j. We get final result as 1 9 2 8 3 7 4 6 5.

C++

 `// C++ program to print the array in given order ` `#include ` `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

 ` ``\$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 ` `?> `

Output:

```1 9 2 8 3 7 4 6 5
```

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