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
{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}.
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Below are implementations of this simple approach.
C++ Implementation of Sort an array in wave form:
c++
// A C++ program to sort an array in wave form using
// a sorting function
#include<iostream>
#include<algorithm>
using namespace std;
// A utility method to swap two numbers.
void swap(int *x, int *y)
{
int temp = *x;
*x = *y;
*y = temp;
}
// This function sorts arr[0..n-1] in wave form, i.e.,
// arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= arr[5]..
void sortInWave(int arr[], int n)
{
// Sort the input array
sort(arr, arr+n);
// Swap adjacent elements
for (int i=0; i<n-1; i += 2)
swap(&arr[i], &arr[i+1]);
}
// Driver program to test above function
int main()
{
int arr[] = {10, 90, 49, 2, 1, 5, 23};
int n = sizeof(arr)/sizeof(arr[0]);
sortInWave(arr, n);
for (int i=0; i<n; i++)
cout << arr[i] << " ";
return 0;
}
Output:
2 1 10 5 49 23 90
JAVA Implementation of Sort an array in wave form:
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[])
{
Test ob = new Test();
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 + " ");
}
}
Output:
2 1 10 5 49 23 90
PYTHON
python
# Python function to sort the array arr[0..n-1] in wave form,
# i.e., arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= arr[5]
def sortInWave(arr, n):
#sort the array
arr.sort()
# Swap adjacent elements
for i in range(0,n-1,2):
arr[i], arr[i+1] = arr[i+1], arr[i]
# Driver progrM
arr = [10, 90, 49, 2, 1, 5, 23]
sortInWave(arr, len(arr))
for i in range(0,len(arr)):
print arr[i],
Output:
2 1 10 5 49 23 90
The time complexity of the above solution is O(nLogn) if a O(nLogn) sorting algorithm like Merge Sort, Heap Sort, .. etc is used.
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