**Objective**

Today, we are learning about an algorithmic concept called recursion. Check out the Tutorial tab for learning materials and an instructional video.

**Recursive Method for Calculating Factorial**

**Function Description**

Complete the factorial function in the editor below. Be sure to use recursion.

a factorial has the following parameter:

- int n: an integer

**Returns**

- int: the factorial of

**Note:**If you fail to use recursion or fail to name your recursive function factorial or Factorial, you will get a score of 0.

**Input Format**

A single integer, n (the argument to pass to factorial).

**Constraints**

- 2 <= n <= 12
- Your submission must contain a recursive function named factorial.

**Sample Input**

3

**Sample Output**

6

**Explanation**

Consider the following steps. After the recursive calls from steps 1 to 3, results are accumulated from steps 3 to 1.

1. factorial(3) = factorial(2) = 3 * 2 = 6

2. factorial)2) = factorial(1) = 2 * 1 = 2

3. factorial(1) = 1

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**Tip:**Always try to implement your own logic this will help you to solve and build a logic. Before copying the program I recommended please read this full article, this will help you to build your own logic.

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## Day 9 Recursion Hackerrank Solution in C

```
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int factorial(int num);
int main() {
int n;
cin >> n;
cout << factorial(n) << endl;
return 0;
}
int factorial(int num) {
if (num == 1) {
return 1;
} else {
return (num * (factorial(num - 1)));
}
}
```

### What is Recursion

According to Wikipedia Recursion occurs when a thing is defined in terms of itself or of its type. or in simple words in terms of Function, when the Function Call itself is Called Recursion

**The syntax of Recursion:**So as we already discuss when a function calls it self-called Recursion.

```
void Recursion();
int main() {
Recursion()
}
void Recursion() {
Recursion();
}
```

### Explanation of Recursion Hackerrank Solution

So we are taking an example of the factorial program with Recursion. Below is the recursion program of factorial. Let's take a value of num as 5, as we know that if we want to the factorial of any number we need to multiply all numbers from 1 to number like

In the return statement Here 5 * (factorial(num-1)) means 5 * 4 and again number reduces by 1 and 5 * 4 * 3 and repeats the process again and again. So this way we can find our solution. I hope you got the problem statement and logic of the problem, Now we can solve the problem. try to solve the Fibonacci problem with the help of recursion.

**5 * 4 * 3 * 2 * 1 = 120.**```
int factorial(int num) // fuction num = 5
{
if (num == 1) {
return 1;
} else {
return (num * (factorial(num - 1))); //Recursion
}
}
```

In the return statement Here 5 * (factorial(num-1)) means 5 * 4 and again number reduces by 1 and 5 * 4 * 3 and repeats the process again and again. So this way we can find our solution. I hope you got the problem statement and logic of the problem, Now we can solve the problem. try to solve the Fibonacci problem with the help of recursion.

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