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Rearrange array such that even positioned are greater than odd

Given an array A of n elements, sort the array according to the following relations :
 A[i] >= A[i-1] , if i is even.
 A[i] <= A[i-1] , 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.



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

Below is the implementation of above approach:

C++

// 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 Code
int main()
{
    int A[] = { 1, 3, 2, 2, 5 };
    int n = sizeof(A) / sizeof(A[0]);
    assign(A, n);
    return 0;
}

Java

// Java program to rearrange the elements
// in array such that even positioned are
// greater than odd positioned elements
import 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

# 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 Code
A = [ 1, 3, 2, 2, 5 ]
n = len(A)
assign(A, n)
  
# This code is contributed by "Sharad_Bhardwaj".

C#

// C# program to rearrange the elements
// in array such that even positioned are
// greater than odd positioned elements
using 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
// 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.
?>


Output:

  1 5 2 3 2


This article is attributed to GeeksforGeeks.org

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