Data Structures

LFU Cache Variant

Difficulty

Asked at Citadel Securities

Theory: Data Structures You Implement, Not Import

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xxx xxx x xxxxxxx xxxx xxxxx xxxxxx xxxx xxxxxxxx xxxxx: xxx xxxxx xx xxx-xxx xxxxxxx, xx xxxxx xxxxxxxxx xxxxxxxx xxx xxxxx xxxxxx xxxxxxxx, xxxxxxx xxxxxxx xxx xxx xxxxx xxx xxxxx xxxxx. xxx xxxxxxxxx-xxxxx xxxxxxxxxxx xx xxx xxxxxxx xxxx xxxxx xxxxxxxxx, xxxxxxx xxxxx xx xx (x(x)) xxxxx x xxxx xxxxxx.

xxxxxxxxx x xxxxx xxxxxxxx(xxxxxxxx) xxxx xxx xxxxxxx:

xxx(xxx): xxxxxx xxx xxxxx xxxxxx xxxxx xxx, xx -x xx xxxxxx. x xxxxxxxxxx xxx xxxxxx xx x xxx xxx xxxxxx xxx xxx'x xxxxxxxxx xx x.
xxx(xxx, xxxxx): xxxxxx xx xxxxxx xxx. xx xxxxxx xxxx xxxxxx xx x xxx (xxxxxxxxx + x). x xxx xxx xxxxxx xxxx xxxxxxxxx x. xx xxxxxxxxx x xxx xxx xxxxx xxxxxx xxxxxxxx, xxxxx xxxxx xxx xxxxx xxxxxxxxxx xxxx xxx; xx xxxxxxx xxxx xxx xx xxx xxxxxx xxxxxxxxx, xxxxx xxx xxxxx xxxxxxxx xxxx xxxxx xxxx.

xxx xxxxx xxxxx xxxx xxxxx xxxxxxx xxx xxx_xxx(xxxxxxxx, xxx) xxxxxx xxxxxxx xx xxx xxxxxxxx (xx xxx xxxxxx xx): xxxx xx xx ("xxx", xxx) xx ("xxx", xxx, xxxxx), xxx xxx xxxxxx xxxxxxx xxx xxxxxx xxx xx, xxxx xxxx xxxxxxxx xxx xxxx.

xxxxxxxx

xxx_xxx(x, [("xxx", x, x), ("xxx", x, x), ("xxx", x), ("xxx", x, x), ("xxx", x), ("xxx", x), ("xxx", x, x), ("xxx", x), ("xxx", x), ("xxx", x)])
# [xxxx, xxxx, x, xxxx, -x, x, xxxx, -x, x, x]
# xxx(x, x) xxxxxx xxx x (xxxxxxxxx x xx xxx x xx x); xxx(x, x) xxxx xxxx x
# xxx x xxxx xx xxxxxxxxx x xxx xxxxxx xxx x, xxx xxxxx xxxxxxxx xxxx

xxx_xxx(x, [("xxx", x, xx), ("xxx", x, xx), ("xxx", x, xx), ("xxx", x, xx), ("xxx", x), ("xxx", x), ("xxx", x)])
# [xxxx, xxxx, xxxx, xxxx, -x, xx, xx]
# xxxxxxxx xxx x xxxxx xx xx xxxxxxxxx x, xx xxx(x, xx) xxxxxx xxx x

xxxxxxxxxxx

x <= xxxxxxxx <= xxxxx; xx xx (x xxxxx xx^x) xxxxxxxxxx.
xxxx xxx xxxxxx xxx xxx-xxxxxxxx xxxxxxxx, xx -x xx xxxxxxxxxxx.
xxxx xxxxxxxxxx xxxx xxx xx (x(x)) xxxx. xxxxxxxx xxx xxxxxxx xxx xxx xxxxxxx xxxxxxxxx xx xxxxxxxx xxxx xx (x(xxxxxxxx)) xxx xxxxxxxx xxx xxxx xxx xxxxxx xxx xxxxxxx xxxxxx xxxx.

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Language: Pythonrun_ops

class LFUCache:
    def __init__(self, capacity):
        """..."""
        # ...
        pass

    def get(self, key):
        """..."""
        # ...
        pass

    def put(self, key, value):
        """..."""
        # ...
        pass


# ...
def run_ops(capacity, ops):
    cache = LFUCache(capacity)
    out = []
    for op in ops:
        if op[0] == "get":
            out.append(cache.get(op[1]))
        else:
            cache.put(op[1], op[2])
            out.append(None)
    return out

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