LRU 缓存

from collections import OrderedDict

def solve():
    d = OrderedDict()
    evicted = '-'
    def put(k):
        nonlocal evicted
        if k in d:
            d.move_to_end(k)
        d[k] = 1
        if len(d) > 2:
            evicted, _ = d.popitem(last=False)
    put('a')
    put('b')
    put('c')
    return evicted