[해커랭크(Hackerrank)/30 Days of Code/파이썬3(python3)] Day 9: Recursion 3

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

Recursive Method for Calculating Factorial 

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

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

Input Format

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

Constraints

• Your submission must contain a recursive function named factorial.

Output Format

Print a single integer denoting .

Sample Input

3

Sample Output

6

Explanation

Consider the following steps:

From steps  and , we can say ; then when we apply the value from  to step , we get . Thus, we print  as our answer.

풀이

#!/bin/python3

import math
import os
import random
import re
import sys

# Complete the factorial function below.
def factorial(n):
    return 1 if n == 1 else n * factorial(n - 1)

if __name__ == '__main__':
    fptr = open(os.environ['OUTPUT_PATH'], 'w')

    n = int(input())

    result = factorial(n)

    fptr.write(str(result) + '\n')

    fptr.close()

설명

처음 보면 멘붕을 야기하는 재귀형 함수 문제이다. 처음 봤을 때는 재귀함수를 잘 이해하기 힘든데 조건문이 끝나기 전까지 값을 대입시키지 않은 채로 반환값들을 쭉 나열해놓은 다음에 주어진 연산을 수행하면 조금 이해하기 쉽다.