# Rearrange array such that even positioned are greater than odd

Given an array arr[] of N elements, sort the array according to the following relations:

• arr[i] >= arr[i – 1], if i is even, âˆ€ 1 <= i < N
• arr[i] <= arr[i – 1], if i is odd, âˆ€ 1 <= i < N

Print the resultant array.

Examples:

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

• For i = 1, arr[1] <= arr[0]. So, 1 <= 2.
• For i = 2, arr[2] >= arr[1]. So, 2 >= 1.
• For i = 3, arr[3] <= arr[2]. So, 1 <= 2.

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

• For i = 1, arr[1] <= arr[0]. So, 1 <= 3.
• For i = 2, arr[2] >= arr[1]. So, 2 >= 1.

Approach: To solve the problem, follow the below idea:

Observe that array consists of [n/2] even positioned elements. If we assign the largest [n/2] elements to the even positions and the rest of the elements to the odd positions, our problem is solved. Because element at the odd position will always be less than the element at the even position as it is the maximum element and vice versa. Sort the array and assign the first [n/2] elements at even positions.

Below is the implementation of the above approach:

## C++

 `#include ``using` `namespace` `std;` `// function to rearrange the elements in array such that``// even positioned are greater than odd positioned elements``void` `assign(``int` `arr[], ``int` `N)``{``    ``// Sort the array``    ``sort(arr, arr + N);` `    ``int` `ans[N];``    ``int` `ptr1 = 0, ptr2 = N - 1;``    ``for` `(``int` `i = 0; i < N; i++) {``        ``// Assign even indexes with maximum elements``        ``if` `(i % 2 == 0)``            ``ans[i] = arr[ptr2--];``        ``// Assign odd indexes with remaining elements``        ``else``            ``ans[i] = arr[ptr1++];``    ``}` `    ``// Print result``    ``for` `(``int` `i = 0; i < N; i++)``        ``cout << ans[i] << ``" "``;``}` `// Driver Code``int` `main()``{``    ``int` `arr[] = { 1, 2, 2, 1 };``    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``assign(arr, N);``    ``return` `0;``}`

## C

 `#include ``#include ` `// Compare function for qsort``int` `cmpfunc(``const` `void``* a, ``const` `void``* b)``{``    ``return` `(*(``int``*)a - *(``int``*)b);``}` `// function to rearrange the elements in array such that``// even positioned are greater than odd positioned elements``void` `assign(``int` `arr[], ``int` `N)``{``    ``// Sort the array``    ``qsort``(arr, N, ``sizeof``(``int``), cmpfunc);` `    ``int` `ans[N];``    ``int` `ptr1 = 0, ptr2 = N - 1;``    ``for` `(``int` `i = 0; i < N; i++) {``        ``// Assign even indexes with maximum elements``        ``if` `(i % 2 == 0)``            ``ans[i] = arr[ptr2--];``        ``// Assign odd indexes with remaining elements``        ``else``            ``ans[i] = arr[ptr1++];``    ``}` `    ``// Print result``    ``for` `(``int` `i = 0; i < N; i++)``        ``printf``(``"%d "``, ans[i]);``}` `// Driver Code``int` `main()``{``    ``int` `arr[] = { 1, 2, 2, 1 };``    ``int` `N = ``sizeof``(arr) / ``sizeof``(arr[0]);``    ``assign(arr, N);``    ``return` `0;``}` `// This code is contributed by Sania Kumari Gupta`

## Java

 `import` `java.io.*;``import` `java.util.*;` `class` `GFG {``    ``// function to rearrange the elements``    ``// in array such that even positioned are``    ``// greater than odd positioned elements``    ``static` `void` `assign(``int` `arr[], ``int` `N)``    ``{``        ``// Sort the array``        ``Arrays.sort(arr);` `        ``int` `ans[] = ``new` `int``[N];``        ``int` `ptr1 = ``0``, ptr2 = N - ``1``;``        ``for` `(``int` `i = ``0``; i < N; i++) {` `            ``// Assign even indexes with maximum elements``            ``if` `(i % ``2` `== ``0``)``                ``ans[i] = arr[ptr2--];` `            ``// Assign odd indexes with remaining elements``            ``else``                ``ans[i] = arr[ptr1++];``        ``}` `        ``// Print result``        ``for` `(``int` `i = ``0``; i < N; i++)``            ``System.out.print(ans[i] + ``" "``);``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String args[])``    ``{``        ``int` `arr[] = { ``1``, ``2``, ``2``, ``1` `};``        ``int` `N = arr.length;``        ``assign(arr, N);``    ``}``}` `// This code is contributed by Nikita Tiwari.`

## C#

 `using` `System;` `class` `GFG {``    ``// function to rearrange the elements``    ``// in array such that even positioned are``    ``// greater than odd positioned elements``    ``static` `void` `assign(``int``[] arr, ``int` `N)``    ``{``        ``// Sort the array``        ``Array.Sort(arr);` `        ``int``[] ans = ``new` `int``[N];``        ``int` `ptr1 = 0, ptr2 = N - 1;``        ``for` `(``int` `i = 0; i < N; i++) {` `            ``// Assign even indexes with maximum elements``            ``if` `(i % 2 == 0)``                ``ans[i] = arr[ptr2--];` `            ``// Assign odd indexes with remaining elements``            ``else``                ``ans[i] = arr[ptr1++];``        ``}` `        ``// Print result``        ``for` `(``int` `i = 0; i < N; i++)``            ``Console.Write(ans[i] + ``" "``);``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main()``    ``{``        ``int``[] arr = { 1, 2, 2, 1 };``        ``int` `N = arr.Length;``        ``assign(arr, N);``    ``}``}` `// This code is contributed by vt_m.`

## Javascript

 ``

## PHP

 ``

## Python3

 `# function  to rearrange the``# elements in array such that``# even positioned are greater``# than odd positioned elements``def` `assign(arr, N):``    ` `    ``# Sort the array``    ``arr.sort()``    ` `    ``ans ``=` `[``0``] ``*` `N``    ``ptr1 ``=` `0``    ``ptr2 ``=` `N ``-` `1``    ``for` `i ``in` `range``(N):``        ` `        ``# Assign even indexes with``        ``# maximum elements``        ``if` `i ``%` `2` `=``=` `0``:``            ``ans[i] ``=` `arr[ptr2]``            ``ptr2 ``=` `ptr2 ``-` `1``        ` `        ``# Assign odd indexes with``        ``# remaining elements``        ``else``:``            ``ans[i] ``=` `arr[ptr1]``            ``ptr1 ``=` `ptr1 ``+` `1``            ` `    ``# Print result``    ``for` `i ``in` `range``(N):``        ``print``(ans[i], end ``=` `" "``)` `# Driver Code``arr ``=` `[ ``1``, ``2``, ``2``, ``1``]``N ``=` `len``(arr)``assign(arr, N)` `# This code is contributed by "Sharad_Bhardwaj".`

Output
`2 1 2 1 `

Time Complexity: O(N * log N), where N is the size of input array arr[].
Auxiliary Space: O(N)

Approach 2: Rearranging array by swapping elements

One other approach is to traverse the array from the first element till N – 1 and swap the element with the next one if the condition is not satisfied. This is implemented as follows:

## C++

 `#include ``using` `namespace` `std;` `// function to rearrange the elements in array such that``// even positioned are greater than odd positioned elements``void` `rearrange(``int` `arr[], ``int` `N)``{``    ``for` `(``int` `i = 0; i < N; i += 2) {``          ``// Compare it with the previous element``        ``if` `(i > 0 && arr[i - 1] > arr[i])``            ``swap(arr[i - 1], arr[i]);``        ` `          ``// Compare it with the next element``        ``if` `(i < N - 1 && arr[i + 1] > arr[i])``            ``swap(arr[i + 1], arr[i]);``    ``}``}` `int` `main()``{``      ``// Sample Input``    ``int` `N = 4;``    ``int` `arr[] = { 1, 2, 2, 1 };``      ` `    ``rearrange(arr, N);``    ` `      ``for` `(``int` `i = 0; i < N; i++)``        ``cout << arr[i] << ``" "``;``    ``cout << ``"\n"``;``    ``return` `0;``}`

## Java

 `import` `java.io.*;` `class` `GFG {``    ``// function to rearrange the elements in array such that``    ``// even positioned are greater than odd positioned elements``    ``static` `void` `rearrange(``int``[] arr, ``int` `N) {``        ``for` `(``int` `i = ``0``; i < N; i += ``2``) {``            ``// Compare it with the previous element``            ``if` `(i > ``0` `&& arr[i - ``1``] > arr[i]) {``                ``int` `temp = arr[i - ``1``];``                ``arr[i - ``1``] = arr[i];``                ``arr[i] = temp;``            ``}` `            ``// Compare it with the next element``            ``if` `(i < N - ``1` `&& arr[i + ``1``] > arr[i]) {``                ``int` `temp = arr[i + ``1``];``                ``arr[i + ``1``] = arr[i];``                ``arr[i] = temp;``            ``}``        ``}``    ``}` `    ``public` `static` `void` `main(String[] args) {``        ``// Sample Input``        ``int` `N = ``4``;``        ``int``[] arr = { ``1``, ``2``, ``2``, ``1` `};` `        ``rearrange(arr, N);` `        ``for` `(``int` `i = ``0``; i < N; i++)``            ``System.out.print(arr[i] + ``" "``);``        ``System.out.println();``    ``}``}` `// This code is contributed by avanitrachhadiya2155`

## C#

 `// C# program to rearrange the elements``// in the array such that even positioned are``// greater than odd positioned elements``using` `System;``class` `GFG {``    ``// function to rearrange the elements in array such that``    ``// even positioned are greater than odd positioned``    ``// elements``    ``static` `void` `Rearrange(``int``[] arr, ``int` `N)``    ``{``        ``for` `(``int` `i = 0; i < N; i += 2) {``            ``// Compare it with the previous element``            ``if` `(i > 0 && arr[i - 1] > arr[i]) {``                ``int` `temp = arr[i - 1];``                ``arr[i - 1] = arr[i];``                ``arr[i] = temp;``            ``}` `            ``// Compare it with the next element``            ``if` `(i < N - 1 && arr[i + 1] > arr[i]) {``                ``int` `temp = arr[i + 1];``                ``arr[i + 1] = arr[i];``                ``arr[i] = temp;``            ``}``        ``}``    ``}` `    ``static` `void` `Main()``    ``{``        ``// Sample Input``        ``int` `N = 4;``        ``int``[] arr = { 1, 2, 2, 1 };` `        ``Rearrange(arr, N);` `        ``for` `(``int` `i = 0; i < N; i++)``            ``Console.Write(arr[i] + ``" "``);``        ``Console.WriteLine();``    ``}``}` `// This code is contributed by shivanisinghss2110`

## Javascript

 `// function to rearrange the elements in array such that``// even positioned are greater than odd positioned elements``function` `rearrange(arr, N) {``    ``for` `(let i = 0; i < N; i += 2) {``        ``// Compare it with the previous element``        ``if` `(i > 0 && arr[i - 1] > arr[i]) {``            ``[arr[i - 1], arr[i]] = [arr[i], arr[i - 1]];``        ``}` `        ``// Compare it with the next element``        ``if` `(i < N - 1 && arr[i + 1] > arr[i]) {``            ``[arr[i], arr[i + 1]] = [arr[i + 1], arr[i]];``        ``}``    ``}``}` `// Sample Input``const N = 4;``const arr = [1, 2, 2, 1];` `rearrange(arr, N);` `console.log(arr.join(``" "``));`

## Python3

 `# function to rearrange the elements in array such that``# even positioned are greater than odd positioned elements`  `def` `rearrange(arr, N):``    ``for` `i ``in` `range``(``0``, N, ``2``):``        ``# Compare it with the previous element``        ``if` `i > ``0` `and` `arr[i ``-` `1``] > arr[i]:``            ``arr[i ``-` `1``], arr[i] ``=` `arr[i], arr[i ``-` `1``]` `        ``# Compare it with the next element``        ``if` `i < N ``-` `1` `and` `arr[i ``+` `1``] > arr[i]:``            ``arr[i], arr[i ``+` `1``] ``=` `arr[i ``+` `1``], arr[i]`  `# Sample Input``N ``=` `4``arr ``=` `[``1``, ``2``, ``2``, ``1``]` `rearrange(arr, N)` `for` `i ``in` `range``(N):``    ``print``(arr[i], end``=``" "``)``print``()`

Output
```4 2 3 2 5
```

Time Complexity: O(N), where N is the size of input array arr[].
Auxiliary Space: O(1)

Previous
Next