Given two sequences A, B, count number of unique ways in sequence A, to form a subsequence that is identical to the sequence B.

Given two sequences A, B, count number of unique ways in sequence A, to form a subsequence that is identical to the sequence B.

Input 1:
    A = "abc"
    B = "abc"
    

Output 1:
    1

Explanation 1:
    Both the strings are equal.

Input 2:
    A = "rabbbit" 
    B = "rabbit"

Output 2:
    3

Explanation 2:
    These are the possible removals of characters:
        => A = "ra_bbit" 
        => A = "rab_bit" 
        => A = "rabb_it"
         

    Note: "_" marks the removed character.