30 Days of Code - Day 9: Recursion

Objective

Today, we’re learning and practicing an algorithmic concept called Recursion. Check out the Tutorial tab for learning materials and an instructional video!

Task

Write a factorial function that takes a positive integer, N as a parameter and prints the result of N! (N factorial).

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.

Output Format

Print a single integer denoting N!.

Sample

3

6

Explanation

Consider the following steps:

1. factorial(3) = 3 * factoria(2)
2. factorial(2) = 2 * factoria(1)
3. `factorial(1) = 1

From steps 2 and 3, we can say factorial(2) = 2 * 1 = 2; then when we apply the value from factorial(2) to step 1, we get factorial(3) = 3 * 2 * 1 = 6. Thus, we print 6 as our answer.

Solution

package main

import "fmt"

func main() {
  var N int
  fmt.Scan(&N)

  fmt.Println(factorial(N))
}

func factorial(n int) int {
  if n == 1 {
    return 1
  }

  return n * factorial(n-1)
}