Sum of First N Natural Numbers Using Recursion

Given a number n, find the sum of the first n natural numbers using recursion.
Examples:

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

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

Approach:

To find the sum of the first n natural numbers using recursion, we define a function recurSum(n-1).

At each step, the function adds the current number n to the sum of all smaller numbers by calling recurSum(n-1).
The recursion continues until the base case is reached, where n = 0, at which point the function returns 0 to stop further calls.
As the recursive calls return back, the intermediate sums are combined step by step, eventually producing the total sum of the first n natural numbers.

#include <iostream>
using namespace std;

int recurSum(int n){
    
    // base case
    if (n == 0)
        return 0;
        
    // recursive case
    return n + recurSum(n - 1);
}

int main(){
    int n = 3;
    cout << recurSum(n);
    return 0;
}

class GFG {
    public static int recurSum(int n){
        
        // base case
        if (n == 0)
            return 0;
            
        // recursive case
        return n + recurSum(n - 1);
    }

    public static void main(String args[]){
        int n = 3;
        System.out.println(recurSum(n));
    }
}

def recurSum(n):
    
    # base case
    if n == 0:
        return 0
        
        # recursive case
    return n + recurSum(n - 1)


# Driver code
if __name__ == "__main__":
    n = 3
    print(recurSum(n))

using System;

class GFG {
    public static int recurSum(int n){
        
        // base case
        if (n == 0)
            return 0;
            
        // recursive case
        return n + recurSum(n - 1);
    }

   
    public static void Main(){
        int n = 3;
        Console.WriteLine(recurSum(n));
    }
}

function recurSum(n) {
    
    // base case
    if (n == 0)
        return 0;
        
    // recursive case
    return n + recurSum(n - 1);
}

// Driver code
let n = 3;
console.log(recurSum(n));

6

Time Complexity: O(n)
Space Complexity: O(n) Recursive Space