sort.py

"""
Test:
  Given two strings, `a` and `b`. Sort the letters in `a` by the order of letters in `b`.
  For example:
    a = "ssttexeste"
    b = "test"
    result = "ttteeesssx"
"""

def a_by_b(a, b):
  pass

a = "adlkfhxaxjxkxhxfwkhkjfhjkahjksedeheflhadslfkhdfjkadhjhdhskghdjdjkhskkhjokhkshakhlhfkjdshjfkshhkskskss"
b = "alskdjfhg"

assert a_by_b(a, b) == "aaaaaallllssssssssssskkkkkkkkkkkkkkkkkkkkdddddddddjjjjjjjjjjjffffffffhhhhhhhhhhhhhhhhhhhhhgxxxxxweeeo"

In JS:

a.split('').map(function(c) { var i = b.indexOf(c); return i == -1 ? Infinity : i; }).sort().map(function(i) { return b[i]; }).join('');

In Ruby:

a.chars.map { |c| b.index(c) || Float::INFINITY }.sort.map { |i| i == Float::INFINITY ? nil : b[i] }.join

Letters in a but not in b are simply dropped.

The performance is way worse than https://gist.github.com/tomhennigan/32e0d6ec4e25311bfd11 because of the number of loops and nested loops, but you can't have everything :P