Lexicographical smallest alternate Array

Given an array arr[] of distinct elements, the task is to rearrange the array such that it is lexicographically smallest and of the form arr[0] > arr[1] < arr[2] > arr[3] < …

Examples:

Input: arr[] = {3, 2, 1, 4, 5}
Output: 2 1 4 3 5

Input: arr[] = {10, 22}
Output: 22 10

Approach: In order to get the lexicographically smallest array, we can choose the minimum element as the first element but that will not satisfy the condition where the first element has to be strictly greater than the second element.
Now, the second-best choice is to choose the second minimum from the array and the only element which is smaller than it is the smallest element which will be the second element of the array.
Apply the same process for the rest of the array elements, choose the second minimum of the remaining elements and then choose the minimum for every two consecutive positions which can be obtained by first sorting the given array then swapping every two consecutive elements.

Below is the implementation of the above approach:

C++

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to print the
// contents of an array
void printArr(int arr[], int n)
{
    for (int i = 0; i < n; i++) {
        cout << arr[i] << " ";
    }
}
  
// Function to find the lexicographically
// smallest alternating array
void smallestArr(int arr[], int n)
{
  
    // Sort the array
    sort(arr, arr + n);
  
    // Swap every two consecutive elements
    for (int i = 0; i + 1 < n; i = i + 2) {
        swap(arr[i], arr[i + 1]);
    }
  
    // Print the re-arranged array
    printArr(arr, n);
}
  
// Driver code
int main()
{
    int arr[] = { 3, 2, 1, 4, 5 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    smallestArr(arr, n);
  
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java implementation of the approach 
import java.util.Arrays;
  
class GFG 
{
  
    // Function to print the
    // contents of an array
    static void printArr(int[] arr, int n) 
    {
        for (int i = 0; i < n; i++)
            System.out.print(arr[i] + " ");
    }
  
    // Function to find the lexicographically
    // smallest alternating array
    static void smallestArr(int[] arr, int n) 
    {
  
        // Sort the array
        Arrays.sort(arr);
  
        // Swap every two consecutive elements
        for (int i = 0; i + 1 < n; i = i + 2
        {
            int temp = arr[i];
            arr[i] = arr[i + 1];
            arr[i + 1] = temp;
        }
  
        // Print the re-arranged array
        printArr(arr, n);
    }
  
    // Driver code
    public static void main(String[] args)
    {
        int[] arr = { 3, 2, 1, 4, 5 };
        int n = arr.length;
        smallestArr(arr, n);
    }
}
  
// This code is contributed by
// sanjeev2552

chevron_right


Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 implementation of the approach 
  
# Function to prthe
# contents of an array
def printArr(arr, n):
    for i in range(n):
        print(arr[i], end = " ");
  
# Function to find the lexicographically
# smallest alternating array
def smallestArr(arr, n):
  
    # Sort the array
    arr.sort();
  
    # Swap every two consecutive elements
    for i in range(0, n - 1, 2):
  
        temp = arr[i];
        arr[i] = arr[i + 1];
        arr[i + 1] = temp;
  
    # Prthe re-arranged array
    printArr(arr, n);
  
# Driver code
if __name__ == '__main__':
  
    arr = [ 3, 2, 1, 4, 5 ];
    n = len(arr);
    smallestArr(arr, n);
      
# This code contributed by Rajput-Ji

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# implementation of the approach 
using System;
      
class GFG 
{
  
    // Function to print the
    // contents of an array
    static void printArr(int[] arr, int n) 
    {
        for (int i = 0; i < n; i++)
            Console.Write(arr[i] + " ");
    }
  
    // Function to find the lexicographically
    // smallest alternating array
    static void smallestArr(int[] arr, int n) 
    {
  
        // Sort the array
        Array.Sort(arr);
  
        // Swap every two consecutive elements
        for (int i = 0; i + 1 < n; i = i + 2) 
        {
            int temp = arr[i];
            arr[i] = arr[i + 1];
            arr[i + 1] = temp;
        }
  
        // Print the re-arranged array
        printArr(arr, n);
    }
  
    // Driver code
    public static void Main(String[] args)
    {
        int[] arr = { 3, 2, 1, 4, 5 };
        int n = arr.Length;
        smallestArr(arr, n);
    }
}
  
// This code is contributed by 29AjayKumar

chevron_right


PHP

filter_none

edit
close

play_arrow

link
brightness_4
code

<?php
// PHP implementation of the approach 
  
// Function to print the 
// contents of an array 
function printArr($arr, $n
    for ($i = 0; $i < $n; $i++)
    
        echo $arr[$i];
        echo " "
    
  
// Function to find the lexicographically 
// smallest alternating array 
function smallestArr($arr, $n
  
    // Sort the array 
    sort($arr); 
  
    // Swap every two consecutive elements 
    for ($i = 0; $i + 1 < $n; $i = $i + 2) 
    
        $temp = $arr[$i];
        $arr[$i] = $arr[$i + 1];
        $arr[$i + 1] = $temp;
    
  
    // Print the re-arranged array 
    printArr($arr, $n); 
  
// Driver code 
$arr = array( 3, 2, 1, 4, 5 ); 
$n = count($arr);
  
smallestArr($arr, $n);
  
// This code is contributed by Naman_Garg.
?>

chevron_right


Output:

2 1 4 3 5


My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.





Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.