Java Program to Sort an array in wave form
Last Updated :
09 Dec, 2022
Given an unsorted array of integers, sort the array into a wave-like array. An array 'arr[0..n-1]' is sorted in wave form if arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= .....
Examples:
Input: arr[] = {10, 5, 6, 3, 2, 20, 100, 80}
Output: arr[] = {10, 5, 6, 2, 20, 3, 100, 80} OR
{20, 5, 10, 2, 80, 6, 100, 3} OR
any other array that is in wave form
Input: arr[] = {20, 10, 8, 6, 4, 2}
Output: arr[] = {20, 8, 10, 4, 6, 2} OR
{10, 8, 20, 2, 6, 4} OR
any other array that is in wave form
Input: arr[] = {2, 4, 6, 8, 10, 20}
Output: arr[] = {4, 2, 8, 6, 20, 10} OR
any other array that is in wave form
Input: arr[] = {3, 6, 5, 10, 7, 20}
Output: arr[] = {6, 3, 10, 5, 20, 7} OR
any other array that is in wave form
A Simple Solution is to use sorting. First sort the input array, then swap all adjacent elements.
For example, let the input array be {3, 6, 5, 10, 7, 20}. After sorting, we get {3, 5, 6, 7, 10, 20}. After swapping adjacent elements, we get {5, 3, 7, 6, 20, 10}.
Below are implementations of this simple approach.
Java
// Java implementation of naive method for sorting
// an array in wave form.
import java.util.*;
class SortWave
{
// A utility method to swap two numbers.
void swap(int arr[], int a, int b)
{
int temp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
}
// This function sorts arr[0..n-1] in wave form, i.e.,
// arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4]..
void sortInWave(int arr[], int n)
{
// Sort the input array
Arrays.sort(arr);
// Swap adjacent elements
for (int i=0; i<n-1; i += 2)
swap(arr, i, i+1);
}
// Driver method
public static void main(String args[])
{
SortWave ob = new SortWave();
int arr[] = {10, 90, 49, 2, 1, 5, 23};
int n = arr.length;
ob.sortInWave(arr, n);
for (int i : arr)
System.out.print(i + " ");
}
}
/*This code is contributed by Rajat Mishra*/
Time complexity: O(n Log n), if a O(nLogn) sorting algorithm like Merge Sort, Heap Sort, .. etc is used.
Auxiliary Space: O(1)
Another approach:
This can be done in O(n) time by doing a single traversal of given array. The idea is based on the fact that if we make sure that all even-positioned (at index 0, 2, 4, ..) elements are greater than their adjacent odd elements, we don't need to worry about odd positioned elements.
The following are simple steps.
- Traverse all even positioned elements of input array, and do following.
- If current element is smaller than previous odd element, swap previous and current.
- If current element is smaller than next odd element, swap next and current.
Below are implementations of the above simple algorithm.
Java
// A O(n) Java program to sort an input array in wave form
import java.util.*;
class SortWave
{
// A utility method to swap two numbers.
void swap(int arr[], int a, int b)
{
int temp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
}
// This function sorts arr[0..n-1] in wave form, i.e.,
// arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4]....
void sortInWave(int arr[], int n)
{
// Traverse all even elements
for (int i = 0; i < n; i+=2)
{
// If current even element is smaller
// than previous
if (i>0 && arr[i-1] > arr[i] )
swap(arr, i-1, i);
// If current even element is smaller
// than next
if (i<n-1 && arr[i] < arr[i+1] )
swap(arr, i, i + 1);
}
}
// Driver program to test above function
public static void main(String args[])
{
SortWave ob = new SortWave();
int arr[] = {10, 90, 49, 2, 1, 5, 23};
int n = arr.length;
ob.sortInWave(arr, n);
for (int i : arr)
System.out.print(i+" ");
}
}
/*This code is contributed by Rajat Mishra*/
Time complexity: O(n)
Auxiliary space: O(1)
Please refer complete article on Sort an array in wave form for more details!
Similar Reads
Javascript Program to Sort an array in wave form Given an unsorted array of integers, sort the array into a wave like array. An array 'arr[0..n-1]' is sorted in wave form if arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= .....Examples: Input: arr[] = {10, 5, 6, 3, 2, 20, 100, 80} Output: arr[] = {10, 5, 6, 2, 20, 3, 100, 80} OR {
4 min read
Java Program to Sort an ArrayList ArrayList is the class provided in the Collection framework. In Java, the collection framework is defined in java.util package. ArrayList is used to dynamically stores the elements. It is more flexible than an array because there is no size limit in ArrayList. ArrayList stores the data in an unorder
6 min read
Sort an array in wave form Given an sorted array arr[] of integers, rearrange the elements into a wave-like array. An array arr[0..n-1] is said to be in wave form if it follows the pattern: \scriptsize arr[0] \geq arr[1] \leq arr[2] \geq arr[3] \leq arr[4] \geq \dots and so on and find the lexicographically smallest one.Note:
4 min read
How to sort an Array of Strings in Java Array Of StringsTo sort an array of strings in Java, we can use Arrays.sort() function. Java // A sample Java program to // sort an array of strings // in ascending and descending // orders using Arrays.sort(). import java.util.Arrays; import java.util.Collections; // Driver Class public class SortE
3 min read
Java Program for Insertion Sort Insertion sort is a simple sorting algorithm that works the way we sort playing cards in our hands. In this article, we will write the program on Insertion Sort in Java.Please refer complete article on Insertion Sort for more details! Algorithm of Insertion SortThe algorithm of Insertion Sort is men
2 min read
Java Program for Bitonic Sort Bitonic Sequence is a sequence is called Bitonic if it is first increasing, then decreasing. In other words, an array arr[0..n-i] is Bitonic if there exists an index i where 0<=i<=n-1 such that x0 <= x1 …..<= xi and xi >= xi+1….. >= xn-1 A sequence, sorted in increasing order is co
4 min read