Check AB.py

"""
---------------------------------------------- Check AB ----------------------------------------

Suppose you have a string, S, made up of only 'a's and 'b's. Write a recursive function that checks 
if the string was generated using the following rules:
    a. The string begins with an 'a'
    b. Each 'a' is followed by nothing or an 'a' or "bb"
    c. Each "bb" is followed by nothing or an 'a'
If all the rules are followed by the given string, return true otherwise return false.

#### Input format :
    String S

#### Output format :
    'true' or 'false'

#### Constraints :
    0 <= |S| <= 1000
    where |S| represents length of string S.

#### Sample Input 1 :
    abb
#### Sample Output 1 :
    true

#### Sample Input 2 :
    abababa
#### Sample Output 2 :
    false
"""

def checkAB(str) : 
    if(len(str) == 0): 
        return True 
    
    if(str[0] == 'a') : 
        if(len(str[1:]) > 1 and str[1:3] == 'bb') : 
            return checkAB(str[3:]) 
        else: 
            return checkAB(str[1:]) 
    else : 
        return False 

# Main     
str=input() 
if(checkAB(str)): 
    print("true") 
else: 
    print("false")