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Rearrange array such that difference of adjacent elements is in descending order
  • Last Updated : 01 Jun, 2020

Given an array a[] with n integers the task is to rearrange the elements of the array in such a way that the differences of the adjacent elements are in descending order.

Examples:

Input : arr[] = {1, 2, 3, 4, 5, 6} 
Output : 6 1 5 2 4 3
Explanation:
For first two elements the difference is abs(6-1)=5
For next two elements the difference is abs(1-5)=4
For next two elements the difference is abs(5-2)=3
For next two elements the difference is abs(2-4)=2
For next two elements the difference is abs(4-3)=1
Hence, difference array is 5, 4, 3, 2, 1.

Input : arr[] = {7, 10, 2, 4, 5}
Output : 10 2 7 4 5 
Explanation:
For first two elements the difference is abs(10-2)=8
For next two elements the difference is abs(2-7)=5
For next two elements the difference is abs(7-4)=3
For next two elements the difference is abs(4-5)=1
Hence, difference array is 8, 5, 3, 1.

Approach:

To solve the problem mentioned above we have to sort the array and then print the elements in the following order for the even-sized array :

a[n], a[1], a[n-1], a[2] ….. a[(n/2)], [(n/2)+1]



And for odd-sized array, we have to print array elements in the following order:

a[n], a[1], a[n-1], a[2] ….. a[(n/2)+1]

Below is the implementation of the above approach:

C++

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// C++ implementation to Rearrange array
// such that difference of adjacent
// elements is in descending order
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to print array in given order
void printArray(int* a, int n)
{
    // Sort the array
    sort(a, a + n);
    int i = 0;
    int j = n - 1;
  
    // Check elements till the middle index
    while (i <= j) {
        // check if length is odd
        // print the middle index at last
        if (i == j) {
            cout << a[i] << " ";
        }
        // Print the remaining elements
        // in the described order
        else {
            cout << a[j] << " ";
            cout << a[i] << " ";
        }
        i = i + 1;
        j = j - 1;
    }
    cout << endl;
}
  
// Driver code
int main()
{
  
    // array declaration
    int arr1[] = { 1, 2, 3, 4, 5, 6 };
  
    // size of array
    int n1 = sizeof(arr1) / sizeof(arr1[0]);
  
    printArray(arr1, n1);
}

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Java

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// Java implementation to Rearrange array
// such that difference of adjacent
// elements is in descending order
import java.util.*;
  
class GFG {
      
// Function to print array in given order
static void printArray(int []a, int n)
{
      
    // Sort the array
    Arrays.sort(a);
      
    int i = 0;
    int j = n - 1;
      
    // Check elements till the 
    // middle index
    while (i <= j)
    {
          
        // Check if length is odd print
        // the middle index at last
        if (i == j)
        {
            System.out.print(a[i] + " ");
        }
          
        // Print the remaining elements
        // in the described order
        else 
        {
            System.out.print(a[j] + " ");
            System.out.print(a[i] + " ");
        }
        i = i + 1;
        j = j - 1;
    }
    System.out.println();
}
      
// Driver code
public static void main (String[] args) 
{
      
    // Array declaration
    int arr1[] = { 1, 2, 3, 4, 5, 6 };
      
    // Size of array
    int n1 = arr1.length;
      
    printArray(arr1, n1);
}    
}
  
// This code is contributed by AnkitRai01

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Python3

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# Python3 implementation to rearrange  
# array such that difference of adjacent 
# elements is in descending order 
  
# Function to print array in given order 
def printArray(a, n): 
      
    # Sort the array 
    a.sort();
      
    i = 0
    j = n - 1
  
    # Check elements till the middle index 
    while (i <= j):
          
        # Check if length is odd print
        # the middle index at last 
        if (i == j):
            print(a[i], end = " "); 
              
        # Print the remaining elements 
        # in the described order 
        else :
            print(a[j], end = " ");
            print(a[i], end = " "); 
          
        i = i + 1
        j = j - 1
  
    print();
  
# Driver code 
if __name__ == "__main__"
  
    # Array declaration 
    arr1 = [ 1, 2, 3, 4, 5, 6 ]; 
  
    # Size of array 
    n1 = len(arr1); 
  
    printArray(arr1, n1); 
  
# This code is contributed by AnkitRai01

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C#

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// C# implementation to rearrange array
// such that difference of adjacent
// elements is in descending order
using System;
  
class GFG {
          
// Function to print array in given order
static void printArray(int []a, int n)
{
          
    // Sort the array
    Array.Sort(a);
          
    int i = 0;
    int j = n - 1;
          
    // Check elements till the 
    // middle index
    while (i <= j)
    {
              
        // Check if length is odd print
        // the middle index at last
        if (i == j)
        {
            Console.Write(a[i] + " ");
        }
              
        // Print the remaining elements
        // in the described order
        else
        {
            Console.Write(a[j] + " ");
            Console.Write(a[i] + " ");
        }
        i = i + 1;
        j = j - 1;
    }
    Console.WriteLine();
}
          
// Driver code
public static void Main (string[] args) 
{
          
    // Array declaration
    int []arr1 = { 1, 2, 3, 4, 5, 6 };
          
    // Size of array
    int n1 = arr1.Length;
          
    printArray(arr1, n1);
}     
}
  
// This code is contributed by AnkitRai01

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Output:

6 1 5 2 4 3

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