Day_9_Recursion_3.md

Day 9: Recursion 3

Problem

Objective

Today, we're learning and practicing an algorithmic concept called Recursion.

Recursive Method for Calculating Factorial

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

On a new line for each query, print Not found if the name has no corresponding entry in the phone book; otherwise, print the full name and phoneNumber in the format name=phoneNumber.

Sample Input

3

Sample Output

6

Explanation

Consider the following steps:

1. factorial(3) = 3 x factorial(2)
2. factorial(2) = 2 x factorial(1)
3. factorial(1) = 1

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

Given code

import math
import os
import random
import re
import sys

# Complete the factorial function below.
def factorial(n):

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

    n = int(input())

    result = factorial(n)

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

    fptr.close()

Solution 1

import math
import os
import random
import re
import sys

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

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

    n = int(input())

    result = factorial(n)

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

    fptr.close()

Solution 2

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()