The title prolly ain't clear at all. You are given a string s and a string t. For every substring s of length |t|, you are to find the number of different characters between the substring of s and t in O(n) or less. It is guaranteed that |t|≤|s|.
Example: s: abac t: ag output: [1, 2, 1]
s: adfjaasd t: asdf output: [3, 4, 4, 4, 4]