30 Days of Code - Day 9: Recursion

Published:
Difficulty: Easy
Platform: HackerRank
URL: https://www.hackerrank.com/challenges/30-recursion
Tags: #challenges-easy #challenges-hackerrank #go

Coding challenges are a great resource for learning coding techniques and improve analytical thinking, this is a collection of challenges from different platforms.

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

input00.txt
3
output00.txt
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

main.go
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)
}