Sum of natural numbers using recursion

Given a number n, find sum of first n natural numbers. To calculate the sum, we will use a recursive function recur_sum().
Examples :

Input : 3
Output : 6
Explanation : 1 + 2 + 3 = 6

Input : 5
Output : 15
Explanation : 1 + 2 + 3 + 4 + 5 = 15

Below is code to find the sum of natural numbers up to n using recursion : 

C++

// C++ program to find the
// sum of natural numbers up
// to n using recursion
#include <iostream>
using namespace std;

// Returns sum of first
// n natural numbers
int recurSum(int n)
{
    if (n <= 1)
        return n;
    return n + recurSum(n - 1);
}

// Driver code
int main()
{
    int n = 5;
    cout << recurSum(n);
    return 0;
}

Java

// Java program to find the
// sum of natural numbers up
// to n using recursion
import java.util.*;
import java.lang.*;

class GFG
{

    // Returns sum of first
    // n natural numbers
    public static int recurSum(int n)
    {
        if (n <= 1)
            return n;
        return n + recurSum(n - 1);
    }

    // Driver code
    public static void main(String args[])
    {
        int n = 5;
        System.out.println(recurSum(n));
    }
}

// This code is contributed by Sachin Bisht

Python

# Python code to find sum
# of natural numbers upto
# n using recursion

# Returns sum of first
# n natural numbers
def recurSum(n):
    if n <= 1:
        return n
    return n + recurSum(n - 1)

# Driver code
n = 5
print(recurSum(n))

C#

// C# program to find the
// sum of natural numbers
// up to n using recursion
using System;

class GFG
{

    // Returns sum of first
    // n natural numbers
    public static int recurSum(int n)
    {
        if (n <= 1)
            return n;
        return n + recurSum(n - 1);
    }

    // Driver code
    public static void Main()
    {
        int n = 5;
        Console.WriteLine(recurSum(n));
    }
}

// This code is contributed by vt_m

PHP

<?php
// PHP program to find the
// sum of natural numbers
// up to n using recursion

// Returns sum of first
// n natural numbers
function recurSum($n)
{
    if ($n <= 1)
        return $n;
    return $n + recurSum($n - 1);
}

// Driver code
$n = 5;
echo(recurSum($n));

// This code is contributed by Ajit.
?>

Javascript

<script>

// JavaScript program to find the
// sum of natural numbers
// up to n using recursion

// Returns sum of first
// n natural numbers
function recurSum(n)
{
    if (n <= 1)
        return n;
    return n + recurSum(n - 1);
}

// Driver code
let n = 5;
document.write(recurSum(n));

// This code is contributed by mohan

</script>

Output :

15 

Time complexity : O(n)

Auxiliary space : O(n)

To solve this question , iterative approach is the best approach because it takes constant or O(1) auxiliary space and the time complexity will be same O(n).