# Common Child

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#
#   Given two strings a and b of equal length, what's the longest string (S) that can be constructed such
#   that it is a child of both?
#   A string x is said to be a child of a string y if x can be formed by deleting 0 or more characters from y.
#   For example, ABCD and ABDC has two children with maximum length 3, ABC and ABD. Note that we will not consider
#   ABCD as a common child because C doesn't occur before D in the second string.
#
#   Input format
#   Two strings a and b, with a newline separating them.
#
#   Constraints
#
#   All characters are upper cased and lie between ASCII values 65-90. The maximum length of the strings is 5000.
#
#   Output format
#   Length of string S.
#
#   Sample Input #0
#   HARRY
#   SALLY
#
#   Sample Output #0
#   2
#   The longest possible subset of characters that is possible by deleting zero or more characters from HARRY
#   and SALLY is AY, whose length is 2.
#
#   Sample Input #1
#   AA
#   BB
#
#   Sample Output #1
#   0
#   AA and BB has no characters in common and hence the output is 0.
#
#   Sample Input #2
#   SHINCHAN
#   NOHARAAA
#
#   Sample Output #2
#   3
#   The largest set of characters, in order, between SHINCHAN and NOHARAAA is NHA.
#
#   Sample Input #3
#   ABCDEF
#   FBDAMN
#
#   Sample Output #3
#   2
#   BD is the longest child of these strings.
#
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