HI, I have a problem to resolve and I don't know how to do it.
The problem goes as follow: I have two strings. Each string is a sequence of letter.
First, I have to return the sequence of letter representing the first string where is deleted the common prefix to both strings.
For example: if I have the strings abcde and abcgh, it returns de, where abc is the common prefix.
Second, I have to return the sequence of letter obtained by deleting all the letters that occurs more than one and keep all the first occurrence of these letters.
For example: abddeggh would equal abdegh
Third,I have to return the sequence of letter by keeping only the first occurrence of the letters in a first sequence of letter and delete all the letters that appear in a second sequence of letters.
For example: asdfgghh and uioasf, would equal dgh.

Can I get help to resolve these three problems please?