# python recursion practice class 12

Contents

## Recursion chapter Revision Notes

Recursion in Python complete Chapter

### Recursion:-

IT is a method function calling where a function can be called ( INVOKE) where a function can be called within its definition.

### Termination condition:

A recursive function has to fulfil an important condition to be used in a program: it has to terminate. A recursive function terminates, if with every recursive call the solution of the problem is downsized and moves towards a base case. A base case is a case, where the problem can be solved without further recursion. A recursion can end up in an infinite loop, if the base case is not met in the calls.

## Example:

4! = 4 * 3!
3! = 3 * 2!
Replacing the calculated values gives us the following expression
4! = 4 * 3 * 2 * 1
In other words, recursion in computer science is a method where the solution to a problem is based on solving smaller instances of the same problem.

## important question:

#### Q1. Write a programme using Recursion to calculate factorial of a number

Ans.   def fact(n):
if n<2:
return1
else:
return(n*fact(n-1))
print(fact(5))
output
120

#### Q2.  using recursion to calculate sum of n numbers.

ans.   def   sum(n):
if n<1:
return 0
else:
return(n + sum(n-1))
print(sum(5))

#### Q3. write a programme using recursion to calculate and display Fibonacci series.

ans.  def fibonacci(x):
if x==o:
return 0
elif x==1:
return   1
else:
fibonacci(x-1)  +   fibonacci(x-2):
print(fibonacci(10))

#### Q4. recursive function to print string in reverse order.

ans.  def  reverse(s):
if len(s)==1:
return s
else:
return(s[-1] + reverse(s[0:len(s)-1))
print(reverse(“abc”))
output
cba

#### Q5. recursive programme to find power of one number  raised to another.

ans.  def   power(x,y):
f=1
for x in range (1,Y+1):
f=f*x
return f
a=5
b=3
c=power(a,b)
print(“power of “,a,”raised to “,b,”=”,c)

#### Q6. programme to count no. of T in file story.txt .

ans.  f=open(“story.txt”,”r”)
count=0
for line in f:
l=len(line)
i=0
while(i<1):
if line[i]==”T”:
count+=1
i+=1
print(” No. of T present=”,count)

#### Q7. to find no. of lines starting with T in story.txt file.

ans.   f=open(“story.txt”,”r”)
count=0
for line in f:
if line==”T”:
count+=1
print(line)
print(” no. of line starting with T=”,count)

#### Q8. write recursive function to print table of 5.

ans.  def   printcount(s,n):
if s==0:
return 10*n
else:
print(s*n)
return(printcount(s+1,n))
n=5
print(printcount(1,n))

### 1 Response

1. November 9, 2020

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