Move-to-Front Encoding

Problem

Encode a string over the given alphabet using the move-to-front transform: for each character output its current index in the alphabet and then move it to the front.

Characters not present in the alphabet are undefined behaviour; assume all input characters belong to it. Return the list of indices.

Hint

Frequently used characters drift towards index 0, which is the point of the transform.

Test cases

case 1

in: ["abc","abc"]

expected: [0,1,2]

case 2

in: ["banana","abn"]

expected: [1,1,2,1,1,1]

case 3

in: ["aaa","abc"]

expected: [0,0,0]

case 4

in: ["cab","abc"]

expected: [2,1,2]

case 5

in: ["","abc"]

expected: []

Starter codePython

def move_to_front_encode(s, alphabet):
    # Your code here
    pass

5 test cases · run your code against them in the editor