Given the length N of the string, we have to find the number of special strings of length N.
A string is called a special string if it consists only of lowercase letters a and b and there is at least one b between two a’s in the string. Since the number of strings may be very large, therefore print it modulo 10^9+7.
Input: N = 2
The number of special string so length 2 are 3 i.e. “ab”, “ba”, “bb”
Input: N = 3
The number of special string so length 3 are 5 i.e. “abb”, “aba”, “bab”, “bba”, “bbb”
To solve the problem mentioned above, the first observation is if the integer N is 0 then there can only be an empty string as the answer, if N is 1 then there can be two string “a” or “b” as an answer but if the value of N is greater than 1 then the answer is equal to the sum of previous two terms. Now to find the count of special strings we run a loop and for each integer i count of the special string of length i is equal to the sum of the count of special strings of length i-1 and count of special strings of length i-2. Store the value of each integer in an array and return the required answer.
Below is the implementation of the above approach:
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- Count number of binary strings such that there is no substring of length greater than or equal to 3 with all 1's
- Count of binary strings of length N having equal count of 0's and 1's and count of 1's ≥ count of 0's in each prefix substring
- Count of same length Strings that exists lexicographically in between two given Strings
- Count of binary strings of length N having equal count of 0's and 1's
- Count of binary strings of length N with even set bit count and at most K consecutive 1s
- Count number of Special Set
- Count the number of special permutations
- Count of sub-strings of length n possible from the given string
- Count of non-palindromic strings of length M using given N characters
- Count of binary strings of given length consisting of at least one 1
- Count ways to increase LCS length of two strings by one
- Maximum count of sub-strings of length K consisting of same characters
- Count of unique palindromic strings of length X from given string
- Count of Binary strings of length N having atmost M consecutive 1s or 0s alternatively exactly K times
- Number of binary strings such that there is no substring of length ≥ 3
- Number of strings of length N with no palindromic sub string
- Find the number of binary strings of length N with at least 3 consecutive 1s
- Number of Binary Strings of length N with K adjacent Set Bits
- Count of Binary Strings of length N such that frequency of 1's exceeds frequency of 0's
- Calculate Sum of ratio of special characters to length of substrings of the given string
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