Implementing an efficent algorithm to find the intersection of two strings

Question

Implement an algorithm that takes two strings as input, and returns the intersection of the two, with each letter represented at most once.

Algo: (considering language used will be c#)

1. Convert both strings into char array
2. take the smaller array and generate a hash table for it with key as the character and value 0
3. Now Loop through the other array and increment the count in hash table if that char is present in it.
4. Now take out all char for hash table whose value is > 0.
5. These are intersection values.

This is an O(n), solution but is uses extra space, 2 char arrays and a hash table

Can you guys think of better solution than this?

Answer 1

How about this ...

var s1 = "aabbccccddd";
var s2 = "aabc";

var ans = s1.Intersect(s2);