Chapter 6.4 recursive functions.md

Chapter 6.4: Recursive Function

Table of Contents:

• Chapter 6.4: Recursive Function
  • Introduction

Introduction

Recursive function is a function which calls itself. A recursive function is generally created to iterate over the dynamic parameter until it reaches the recursion limit. Recursive function contains 2 different elements:

1. recursion limit
2. recursive function call

Basic Syntax

def function_name(params):
    if condition:
        function_name(updated_params)
    else:   # recursion Limit
        return final_value

Example 1: A recursive function that prints out the factorial of a number.

• 5 ! = 5 * 4 * 3 * 2 * 1 = 120
• 0 ! = 1

def factorial(n):
    if n > 0:
        return(n * factorial(n-1))
    return 1

print(factorial(7))     # 5040

Example 2: A recursive function that prints out the first nth item of a fibonacci series 1, 1, 2, 3, 5, 8, 13, 21, 34, ....

def fibonacci(n):
    if n > 1:
        return(fibonacci(n-1) + fibonacci(n-2))
    return n

item = fibonacci(7)

print(item)     # 13

Example 3: A recursive function to convert decimal to binary

def dec2bin(n: int):
    if n != 0:
        return dec2bin(n // 2) * 10 + n % 2
    else:
        return 0

print(dec2bin(14))  # 1110