Alternate elements of an array

Last Updated : 04 Dec, 2024

Given an array arr[], the task is to print every alternate element of the array starting from the first element.

Examples:

Input: arr[] = [10, 20, 30, 40, 50]
Output: 10 30 50
Explanation: Print the first element (10), skip the second element (20), print the third element (30), skip the fourth element(40) and print the fifth element(50).

Input: arr[] = [-5, 1, 4, 2, 12]
Output: -5 4 12

Table of Content

Iterative Approach
Recursive Approach

Iterative Approach

The idea is to start iterating from index 0, print the element at that index, and then increment the index by 2 to move to the next alternate element. Keep on printing the elements till we reach the end of the array.

C++

// Iterate C++ Program to print alternate elements
// of the array

#include <iostream>
#include <vector>
using namespace std;

vector<int> getAlternates(vector<int> &arr) {
    vector<int> res;
  
    // Iterate over all alternate elements 
    for(int i = 0; i < arr.size(); i += 2) {
    	res.push_back(arr[i]);
    }
    return res;
}

int main() {
    vector<int> arr = {10, 20, 30, 40, 50};
    vector<int> res = getAlternates(arr); 
    for(int x: res)
        cout << x << " ";
}

// Iterate C Program to print alternate elements
// of the array

#include <stdio.h>

void getAlternates(int arr[], int n) {
    
    // Iterate over all alternate elements
    for(int i = 0; i < n; i += 2) {
        printf("%d ", arr[i]);
    }
}

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    int size = sizeof(arr) / sizeof(arr[0]);
    getAlternates(arr, size);
    return 0;
}

Java

// Iterate Java Program to print alternate elements
// of the array

import java.util.*;

class GfG {
    static ArrayList<Integer> getAlternates(int[] arr) {
        ArrayList<Integer> res = new ArrayList<>();
      
        // Iterate over all alternate elements
        for (int i = 0; i < arr.length; i += 2) {
            res.add(arr[i]);
        }
        return res;
    }

    public static void main(String[] args) {
        int[] arr = {10, 20, 30, 40, 50};
        ArrayList<Integer> res = getAlternates(arr);
        for (int x : res) {
            System.out.print(x + " ");
        }
    }
}

Python

# Iterate Python Program to print alternate elements
# of the array

def getAlternates(arr):
    res = []
    
    # Iterate over all alternate elements
    for i in range(0, len(arr), 2):
        res.append(arr[i])
    return res

if __name__ == "__main__":
    arr = [10, 20, 30, 40, 50]
    res = getAlternates(arr)
    print(" ".join(map(str, res)))

// Iterate C# Program to print alternate elements
// of the array

using System;
using System.Collections.Generic;

class GfG {
    static List<int> getAlternates(int[] arr) {
        List<int> res = new List<int>();
      
        // Iterate over all alternate elements
        for (int i = 0; i < arr.Length; i += 2) {
            res.Add(arr[i]);
        }
        return res;
    }

    static void Main() {
        int[] arr = { 10, 20, 30, 40, 50 };
        List<int> res = getAlternates(arr);
        foreach (int x in res) {
            Console.Write(x + " ");
        }
    }
}

JavaScript

// Iterate JavaScript Program to print alternate elements
// of the array

function getAlternates(arr) {
    let res = [];
    
    // Iterate over all alternate elements
    for (let i = 0; i < arr.length; i += 2) {
        res.push(arr[i]);
    }
    return res;
}


// Driver Code
const arr = [10, 20, 30, 40, 50];
const res = getAlternates(arr);
console.log(res.join(" "));

Output

10 30 50

Time Complexity: O(n), where n is the number of elements in arr[].
Auxiliary Space: O(1)

Recursive Approach

We can also print the alternate elements using recursion. We start from index = 0, that is the first element of the array and print its value. We then call the recursive function again with the (index + 2) as the current index.

C++

// Recursive C++ Program to print alternate elements
// of the array

#include <iostream>
#include <vector>
using namespace std;

// Recursive function to store all alternate elements
void getAlternatesRec(vector<int> &arr, int idx, vector<int>& res) {
	if(idx < arr.size()) {
    	res.push_back(arr[idx]);
        getAlternatesRec(arr, idx + 2, res);
    }
}

vector<int> getAlternates(vector<int> &arr) {
    vector<int> res;
    getAlternatesRec(arr, 0, res);
    return res;
}

int main() {
    vector<int> arr = {10, 20, 30, 40, 50};
    vector<int> res = getAlternates(arr); 
    for(int x: res)
        cout << x << " ";
}

Java

// Recursive Java Program to print alternate elements
// of the array

import java.util.ArrayList;

class GfG {
    
    // Recursive function to store all alternate elements
    static void getAlternatesRec(int[] arr, int idx, 
                                 ArrayList<Integer> res) {
        if (idx < arr.length) {
            res.add(arr[idx]);
            getAlternatesRec(arr, idx + 2, res);
        }
    }

    static ArrayList<Integer> getAlternates(int[] arr) {
        ArrayList<Integer> res = new ArrayList<>();
        getAlternatesRec(arr, 0, res);
        return res;
    }

    public static void main(String[] args) {
        int[] arr = {10, 20, 30, 40, 50};
        ArrayList<Integer> res = getAlternates(arr);
        for (int x : res) {
            System.out.print(x + " ");
        }
    }
}

Python

# Recursive Python Program to print alternate elements
# of the array

# Recursive function to store all alternate elements
def getAlternatesRec(arr, idx, res):
    if idx < len(arr):
        res.append(arr[idx])
        getAlternatesRec(arr, idx + 2, res)

def getAlternates(arr):
    res = []
    getAlternatesRec(arr, 0, res)
    return res

if __name__ == "__main__":
    arr = [10, 20, 30, 40, 50]
    res = getAlternates(arr)
    print(" ".join(map(str, res)))

// Recursive C# Program to print alternate elements
// of the array

using System;
using System.Collections.Generic;

class GfG {
    
    // Recursive function to store all alternate elements
    static void getAlternatesRec(int[] arr, int idx, 
                                 	List<int> res) {
        if (idx < arr.Length) {
            res.Add(arr[idx]);
            getAlternatesRec(arr, idx + 2, res);
        }
    }

    static List<int> getAlternates(int[] arr) {
        List<int> res = new List<int>();
        getAlternatesRec(arr, 0, res);
        return res;
    }

    static void Main() {
        int[] arr = { 10, 20, 30, 40, 50 };
        List<int> res = getAlternates(arr);
        foreach (int x in res) {
            Console.Write(x + " ");
        }
    }
}

JavaScript

// Recursive JavaScript Program to print alternate
// elements of the array

// Recursive function to store all alternate elements
function getAlternatesRec(arr, idx, res) {
    if (idx < arr.length) {
        res.push(arr[idx]);
        getAlternatesRec(arr, idx + 2, res);
    }
}

function getAlternates(arr) {
    let res = [];
    getAlternatesRec(arr, 0, res);
    return res;
}

// Driver Code
let arr = [10, 20, 30, 40, 50];
let res = getAlternates(arr);
console.log(res.join(" "));

Output

10 30 50

Time Complexity: O(n), where n is the number of elements in arr[].
Auxiliary Space: O(n), for recursive call stack.

Largest element after K operations on Array

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Alternate elements of an array

Iterative Approach

Recursive Approach

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