Check AB.cpp

/*
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 :
1 <= |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

*/

#include<string>
#include<algorithm>

bool checkAB(char input[],int count = 0) {
	// Write your code here
	// base case
    if(*input == '\0') {
        return true;
    }
    
    // corner case
    if(!count) {
        if(input[0] != 'a') {
            return false;
        }
    }
    
    //nth step
    //first Rule
    if(input[0] == 'a') {
        if(input[1] == '\0' or input[1] == 'a' or (input[1] == 'b' and input[2] == 'b')) {
            checkAB(input + 1, count + 1);
        } else {
            return false;
        }
    }
    
    // second Rule
    else if(input[0] == 'b' and input[1] == 'b') {
        if(input[2] == 'a' or input[2] == '\0') {
            checkAB(input + 2,count + 1);
        } else {
            return false;
        }
    }
    
}