Sorted Array to Wave Form (original) (raw)

Last Updated : 11 Feb, 2025

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Given a **sorted array of integers, the task is to **sort the array into a **wave 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[] = {1, 2, 3, 4, 5}
**Output: arr[] = {2, 1, 4, 3, 5}
**Explanation: The output array has the form: arr[0] >= arr[1] <= arr[2] >= arr[3] <= arr[4] >= .....

**Input: arr[] = {2, 4, 7, 8, 9, 10}
**Output: arr[] = {4, 2, 8, 7, 10, 9}

**Approach:

The idea is to utilize the fact that the array is already **sorted. By simply **swapping adjacent elements starting from index 0, we automatically get a wave pattern since each swapped element from an **even index will be **greater than its neighbors, while each swapped element from an **odd index will be **smaller than its neighbors.

Below is the implementation of the above approach:

C++ `

// C++ program to sort an array in wave form. #include<bits/stdc++.h> using namespace std;

// This function sorts arr[0..n-1] in wave form void convertToWave(vector &arr) { int n = arr.size();

// Swap adjacent elements to create wave pattern
for (int i = 0; i < n-1; i += 2) {
    swap(arr[i], arr[i + 1]);
}

}

int main() { vector arr = {1, 2, 3, 4, 5}; convertToWave(arr); for (int i=0; i<arr.size(); i++) cout << arr[i] << " "; return 0; }

Java

// Java program to sort an array in wave form. import java.util.*;

class GfG {

// This function sorts arr[0..n-1] in wave form
static void convertToWave(int[] arr) {
    int n = arr.length;

    // Swap adjacent elements to create wave pattern
    for (int i = 0; i < n - 1; i += 2) {
        int temp = arr[i];
        arr[i] = arr[i + 1];
        arr[i + 1] = temp;
    }
}

public static void main(String[] args) {
    int[] arr = {1, 2, 3, 4, 5};
    convertToWave(arr);
    for (int i = 0; i < arr.length; i++) {
        System.out.print(arr[i] + " ");
    }
}

}

Python

Python program to sort an array in wave form.

This function sorts arr[0..n-1] in wave form

def convertToWave(arr): n = len(arr)

# Swap adjacent elements to create wave pattern
for i in range(0, n - 1, 2):
    arr[i], arr[i + 1] = arr[i + 1], arr[i]

if name == "main": arr = [1, 2, 3, 4, 5] convertToWave(arr) print(" ".join(map(str, arr)))

C#

// C# program to sort an array in wave form. using System;

class GfG {

// This function sorts arr[0..n-1] in wave form
static void convertToWave(int[] arr) {
    int n = arr.Length;

    // Swap adjacent elements to create wave pattern
    for (int i = 0; i < n - 1; i += 2) {
        int temp = arr[i];
        arr[i] = arr[i + 1];
        arr[i + 1] = temp;
    }
}

static void Main(string[] args) {
    int[] arr = {1, 2, 3, 4, 5};
    convertToWave(arr);
    for (int i = 0; i < arr.Length; i++) {
        Console.Write(arr[i] + " ");
    }
}

}

JavaScript

// JavaScript program to sort an array in wave form.

// This function sorts arr[0..n-1] in wave form function convertToWave(arr) { const n = arr.length;

// Swap adjacent elements to create wave pattern
for (let i = 0; i < n - 1; i += 2) {
    let temp = arr[i];
    arr[i] = arr[i + 1];
    arr[i + 1] = temp;
}

}

const arr = [1, 2, 3, 4, 5]; convertToWave(arr); console.log(arr.join(" "));

`

**Time Complexity: O(n)
**Auxiliary Space: O(1)