Function for: https://twitter.com/ftrain/status/267503513477713920

gistfile1.py

def ftrain(l):
    """https://twitter.com/ftrain/status/267503513477713920

    Assumes list will be "deepest" in the center
    """

    # are all elements the same? group together and return
    if len(set(l)) <= 1:
        return l

    # find 'start' of a group
    for k, val in enumerate(l):
        if val != l[0]:
            start = k
            break

    # find 'end' of a group
    for k, val in reversed(list(enumerate(l))):
        if val != l[0]:
            end = k + 1
            break

    out = l[:start]
    out.append(ftrain(l[start:end]))
    out.extend(l[end:])
    return out

l = [1,2,3,3,4,4,2,1]
print ftrain(l)