Python Program to Find Factorial of a Number.

Given a number num, write a Python program to find the factorial of that number. The Factorial of a non-negative number is equal to the multiplication of all integers smaller than or equal to that number.

Example:
Input: num = 5
Output: 120

Explanation: 5*4*3*2*1 = 120

Input: num = 0
Output: 1

Input: num = 7
Output: 5040

Explanation: 7*6*5*4*3*2*1 = 5040

Approach 1: Factorial of a number using a for a loop.

In this approach, the program uses a for loop to iterate through the numbers from 1 to the given number and calculates the factorial by multiplying each number.

Python Code:

# take input for the number
num = int(input("Enter a number: "))

# initialize the factorial to 1
factorial = 1

# use a for loop to calculate the factorial
for i in range(1, num + 1):
    factorial *= i

# print the result
print("The factorial of", num, "is", factorial)

Output:

Enter a number: 5
The factorial of 5 is 120

Time Complexity: O(n)
Space Complexity: O(1)

Approach 2: Factorial of a number using Recursion.

In this approach, the program uses recursion to find the factorial. The factorial function calls itself with the argument n-1 until the base case n=1 is reached, and then returns the result.

Python Code:

# define a recursive function to find the factorial
def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n - 1)

# take input for the number
num = int(input("Enter a number: "))

# call the factorial function to find the factorial
result = factorial(num)

# print the result
print("The factorial of", num, "is", result)

Output:

Enter a number: 5
The factorial of 5 is 120

Time Complexity: O(n)
Space Complexity: O(n)

Approach 3: Factorial of a number using a While loop.

In this approach, the program uses a while loop to calculate the factorial in a similar way as the for loop in approach 1.

Python Code:

# take input for the number
num = int(input("Enter a number: "))

# initialize the factorial to 1
factorial = 1

# initialize the counter to 1
i = 1

# use a while loop to calculate the factorial
while i <= num:
    factorial *= i
    i += 1

# print the result
print("The factorial of", num, "is", factorial)

Output:

Enter a number: 7
The factorial of 7 is 5040

Time Complexity: O(n)
Space Complexity: O(1)

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Python Program to Find Factorial of a Number.

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