Rearrange array such that even positioned are greater than odd - GeeksforGeeks

20 Apr, 2021
Given an array A of n elements, sort the array according to the following relations :  
 
, if i is even.  
 
, if i is odd. Print the resultant array.Examples :  
 
Input : A[] = {1, 2, 2, 1}
Output :  1 2 1 2
Explanation : 
For 1st element, 1  1, i = 2 is even.
3rd element, 1  1, i = 4 is even.

Input : A[] = {1, 3, 2}
Output : 1 3 2
Explanation : 
Here, the array is also sorted as per the conditions. 
1  1 and 2 < 3.
 
Method 1 – 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++
Java
Python3
C#
PHP
Javascript
// C++ program to rearrange the elements// in array such that even positioned are// greater than odd positioned elements#include <bits/stdc++.h>using namespace std; void assign(int a[], int n){    // Sort the array    sort(a, a + n);     int ans[n];    int p = 0, q = n - 1;    for (int i = 0; i < n; i++) {        // Assign even indexes with maximum elements        if ((i + 1) % 2 == 0)            ans[i] = a[q--];         // Assign odd indexes with remaining elements        else            ans[i] = a[p++];    }     // Print result    for (int i = 0; i < n; i++)        cout << ans[i] << " ";} // Driver Codeint main(){    int A[] = { 1, 3, 2, 2, 5 };    int n = sizeof(A) / sizeof(A[0]);    assign(A, n);    return 0;}
// Java program to rearrange the elements// in array such that even positioned are// greater than odd positioned elementsimport java.io.*;import java.util.*; class GFG {     static void assign(int a[], int n)    {         // Sort the array        Arrays.sort(a);         int ans[] = new int[n];        int p = 0, q = n - 1;        for (int i = 0; i < n; i++) {             // Assign even indexes with maximum elements            if ((i + 1) % 2 == 0)                ans[i] = a[q--];             // Assign odd indexes with remaining elements            else                ans[i] = a[p++];        }         // Print result        for (int i = 0; i < n; i++)            System.out.print(ans[i] + " ");    }     // Driver code    public static void main(String args[])    {        int A[] = { 1, 3, 2, 2, 5 };        int n = A.length;        assign(A, n);    }} // This code is contributed by Nikita Tiwari.
# Python3 code to rearrange the# elements in array such that# even positioned are greater# than odd positioned elements def assign(a, n):         # Sort the array    a.sort()         ans = [0] * n    p = 0    q = n - 1    for i in range(n):                 # Assign even indexes with        # maximum elements        if (i + 1) % 2 == 0:            ans[i] = a[q]            q = q - 1                 # Assign odd indexes with        # remaining elements        else:            ans[i] = a[p]            p = p + 1                 # Print result    for i in range(n):        print(ans[i], end = " ") # Driver CodeA = [ 1, 3, 2, 2, 5 ]n = len(A)assign(A, n) # This code is contributed by "Sharad_Bhardwaj".
// C# program to rearrange the elements// in array such that even positioned are// greater than odd positioned elementsusing System; class GFG {     static void assign(int[] a, int n)    {        // Sort the array        Array.Sort(a);         int[] ans = new int[n];        int p = 0, q = n - 1;        for (int i = 0; i < n; i++) {             // Assign even indexes with maximum elements            if ((i + 1) % 2 == 0)                ans[i] = a[q--];             // Assign odd indexes with remaining elements            else                ans[i] = a[p++];        }         // Print result        for (int i = 0; i < n; i++)            Console.Write(ans[i] + " ");    }     // Driver code    public static void Main()    {        int[] A = { 1, 3, 2, 2, 5 };        int n = A.Length;        assign(A, n);    }} // This code is contributed by vt_m.
<?php// PHP program to rearrange// the elements in array such// that even positioned are// greater than odd positioned// elements function assign($a, $n){         // Sort the array    sort($a);     $p = 0; $q = $n - 1;    for ($i = 0; $i < $n; $i++)    {                 // Assign even indexes        // with maximum elements        if (($i + 1) % 2 == 0)            $ans[$i] = $a[$q--];         // Assign odd indexes        // with remaining elements        else            $ans[$i] = $a[$p++];    }     // Print result    for ($i = 0; $i < $n; $i++)        echo($ans[$i] . " ");} // Driver Code$A = array( 1, 3, 2, 2, 5 );$n = sizeof($A);assign($A, $n); // This code is contributed by Ajit.?>
<script> // JavaScript program to rearrange the elements// in array such that even positioned are// greater than odd positioned elements     function assign(a, n)    {          // Sort the array        a.sort();          let ans = [];        let p = 0, q = n - 1;        for (let i = 0; i < n; i++) {              // Assign even indexes with maximum elements            if ((i + 1) % 2 == 0)                ans[i] = a[q--];              // Assign odd indexes with remaining elements            else                ans[i] = a[p++];        }          // Print result        for (let i = 0; i < n; i++)            document.write(ans[i] + " ");    } // Driver code         let A = [ 1, 3, 2, 2, 5 ];        let n = A.length;        assign(A, n);                             </script>
Output: 
1 5 2 3 2
Time Complexity: O(n * log n)
Auxiliary Space: O(n) Method 2 – One other approach is to traverse the array from the second element and swap the element with the previous one if the condition is not satisfied. This is implemented as follows:  
C++
Java
Python3
C#
Javascript
// C++ program to rearrange the elements// in the array such that even positioned are// greater than odd positioned elements#include <bits/stdc++.h>using namespace std; // swap two elementsvoid swap(int* a, int* b){    int temp = *a;    *a = *b;    *b = temp;} void rearrange(int arr[], int n){    for (int i = 1; i < n; i++) {        // if index is even        if (i % 2 == 0) {            if (arr[i] > arr[i - 1])                swap(&arr[i - 1], &arr[i]);        }        // if index is odd        else {            if (arr[i] < arr[i - 1])                swap(&arr[i - 1], &arr[i]);        }    }} int main(){    int n = 5;    int arr[] = { 1, 3, 2, 2, 5 };    rearrange(arr, n);    for (int i = 0; i < n; i++)        cout << arr[i] << " ";    cout << "\n";    return 0;}
// Java program to rearrange the elements// in the array such that even positioned are// greater than odd positioned elementsclass GFG{  public static void rearrange(int[] arr, int n)  {    for(int i = 1; i < n; i++)    {       // if index is even      if(i % 2 == 0)      {        if(arr[i] > arr[i - 1])        {           // swap two elements          int temp = arr[i];          arr[i] = arr[i - 1];          arr[i - 1] = temp;        }      }       // if index is odd      else      {        if (arr[i] < arr[i - 1])        {           // swap two elements          int temp = arr[i];          arr[i] = arr[i - 1];          arr[i - 1] = temp;        }      }    }     for (int i = 0; i < n; i++)    {      System.out.print(arr[i] + " ");    }  }   // Driver code  public static void main(String []args)  {    int n = 5;    int arr[] = {1, 3, 2, 2, 5};    rearrange(arr, n);  }} // This code is contributed by avanitrachhadiya2155
# Python3 program to rearrange# the elements in the array# such that even positioned are# greater than odd positioned elementsdef rearrange(arr, n):     for i in range (1, n):               # if index is even        if (i % 2 == 0):            if (arr[i] > arr[i - 1]):                arr[i - 1], arr[i] = arr[i], arr[i - 1]                 # if index is odd        else:            if (arr[i] < arr[i - 1]):                arr[i - 1], arr[i] = arr[i] , arr[i - 1] if __name__ == "__main__":             n = 5    arr = [1, 3, 2, 2, 5]    rearrange(arr, n);    for i in range (n):        print (arr[i], end = " ")    print ()    # This code is contributed by Chitranayal
// C# program to rearrange the elements// in the array such that even positioned are// greater than odd positioned elementsusing System;class GFG{public static void rearrange(int[] arr, int n){    for(int i = 1; i < n; i++)    {       // if index is even      if(i % 2 == 0)      {          if(arr[i] > arr[i - 1])          {           // swap two elements          int temp = arr[i];          arr[i] = arr[i - 1];          arr[i - 1] = temp;          }      }       // if index is odd      else      {          if (arr[i] < arr[i - 1])          {             // swap two elements            int temp = arr[i];            arr[i] = arr[i - 1];            arr[i - 1] = temp;          }      }    }   for (int i = 0; i < n; i++)  {    Console.Write(arr[i] + " ");  }} // Driver codepublic static void Main(String []args){    int n = 5;    int []arr = {1, 3, 2, 2, 5};    rearrange(arr, n);}} // This code is contributed by shivanisinghss2110
<script> // JavaScript program to rearrange the elements// in the array such that even positioned are// greater than odd positioned elements   function rearrange(arr, n)  {    for(let i = 1; i < n; i++)    {        // if index is even      if(i % 2 == 0)      {        if(arr[i] > arr[i - 1])        {            // swap two elements          let temp = arr[i];          arr[i] = arr[i - 1];          arr[i - 1] = temp;        }      }        // if index is odd      else      {        if (arr[i] < arr[i - 1])        {            // swap two elements          let temp = arr[i];          arr[i] = arr[i - 1];          arr[i - 1] = temp;        }      }    }      for (let i = 0; i < n; i++)    {      document.write(arr[i] + " ");    }  }       // Driver code             let n = 5;    let arr = [1, 3, 2, 2, 5];    rearrange(arr, n);                   </script>
Output: 
1 3 2 5 2
Time Complexity: O(n)
Auxiliary Space: O(1) 
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mohdmohtashimnawaz
ukasp
avanitrachhadiya2155
shivanisinghss2110
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