Recursion in Python

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Recursion is an approach to solve a problem which involves a function calling itself either directly or indirectly. Such a function is known as a recursive function.

Every recursive method must have a base case which would stop calling the function again and again indefinitely, because the function stack has a limit, which is platform dependent.

A Python program to print a string backwards using a recursive function.

def reverse(s, n):
    if n > 0:
        print(s[n], end = '')
        reverse(s, n - 1)
    elif n == 0:
        print(s[0])

s = input('Enter the string: ')
reverse(s, len(s) - 1)

A Python program to calculate ab using a recursive function.

def power(a, b):
    if b == 0:
        return 1
    else:
        return a * power(a, b - 1)

a = int(input('a = '))
b = int(input('b = '))
p = power(a, b)
print('a to the power b: ' + str(p))

A Python program to find the Factorial using a recursive function.

def factorial(n):
    if n == 0 or n == 1:
        return 1
    else:
        return n * factorial(n - 1)

n = int(input('n = '))
f = factorial(n)
print('Factorial: ' + str(f))

A Python program to find the GCD using a recursive function.

def gcd(a, b):
    if b == 0:
        return a
    else:
        return gcd(b, a % b)

a = int(input('a = '))
b = int(input('b = '))
hcf = gcd(a, b)
print('GCD: ' + str(hcf))

A Python program to display Fibonacci Series using a recursive function.

def fibo(n):
    if n == 1:
        return 0
    if n == 2:
        return 1
    return fibo(n - 1) + fibo(n - 2)

n = int(input('Number of terms: '))
for i in range(1, n + 1):
    print(fibo(i), end = ' ')
print()

A Python program to perform Binary Search using a recursive function.

def search(myList, key, low, high):
    if low > high:
        return -1
    mid = (low + high) // 2
    if key == myList[mid]:
        return mid
    elif key < myList[mid]:
        return search(myList, key, low, mid - 1)
    else:
        return search(myList, key, mid + 1, high)

myList = [12, 23, 34, 45, 56, 67, 78]
key = int(input('Element to be searched: '))
index = search(myList, key, 0, len(myList) - 1)
if index >= 0:
    print(str(key) + ' is present at index ' + str(index))
else:
    print(str(key) + ' is not present')
Location: Asansol, West Bengal, India

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