Finding pixels that make an image unique within a list, can you improve on brute force?

Question

Suppose I have a list of strings where each string is

• exactly 4 characters long and
• unique within the list.

For each of these strings I wan

Answer 1

This problem can be solved by trie, or prefix tree.

See Trie - Wikipedia, the free encyclopedia

For the 3 strings in your example:

abcd
abcc
bbcb

will be turned into a trie tree (where ^ denotes the root of the tree):

^--a-b-c-d
 \      \
  \      c
   \
    b-b-c-b

The path to the node where it branch off are the common prefix. The node after the last branch point is what makes a particular string unique. In this case, they are d, c, b.

I assume the order of string is not important for you, that you compares all strings to find the uniqueness, not just the neighboring string.

The complexity should be O(n x m). But this will probably affected by the domain of the characters in your string.