How to form code logic

#1

Not able to understand how to write code for this?

#2

What are the subproblems in this case? The idea is process all characters one by one staring from either from left or right sides of both strings. Let us traverse from right corner, there are two possibilities for every pair of character being traversed.

m: Length of str1 (first string) n: Length of str2 (second string) If last characters of two strings are same, nothing much to do. Ignore last characters and get count for remaining strings. So we recur for lengths m-1 and n-1. Else (If last characters are not same), we consider all operations on ‘str1’, consider all three operations on last character of first string, recursively compute minimum cost for all three operations and take minimum of three values. Insert: Recur for m and n-1 Remove: Recur for m-1 and n Replace: Recur for m-1 and n-1

#3

ok so for insert case why to recur for m and n-1? now like
str1=asds
str2=asdsf
so in this we can insert f in first string right?
Then why to recur for m and n-1??