Sum of natural numbers

//Time complexity O(n) and Space complexity O(n)

int sum_recursive(int n) {

    if(n == 0) {

        return 0;

    }

    return sum_recursive(n - 1) + n;

}

//Time complexity O(n) and Space complexity O(1)

int sum_iterative(int n) {

    int sum = 0;

    for(int i = 1; i <= n; i++) {

        sum += i;

    }

    return sum;

}

    

//Time complexity O(1) and Space complexity O(1)

int sum_usingFormula(int n) {

    return n * (n + 1) / 2;

}