39 lines
989 B
Nim
39 lines
989 B
Nim
# SPDX-FileCopyrightText: 2021 ☭ Emery Hemingway
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# SPDX-License-Identifier: Unlicense
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## An unordered association of items to counts.
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## An item count may be negative, unlike CountTable.
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import tables
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type
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ChangeDescription* = enum
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cdPresentToAbsent,
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cdAbsentToAbsent,
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cdAbsentToPresent,
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cdPresentToPresent
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Bag*[T] = Table[T, int]
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proc change(count: var int; delta: int; clamp: bool): ChangeDescription =
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var
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oldCount = count
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newCount = oldCount + delta
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if clamp:
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newCount = max(0, newCount)
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if newCount == 0:
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result =
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if oldCount == 0: cdAbsentToAbsent
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else: cdPresentToAbsent
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else:
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result =
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if oldCount == 0: cdAbsentToPresent
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else: cdPresentToPresent
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count = newCount
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proc change*[T](bag: var Bag[T]; key: T; delta: int; clamp = false): ChangeDescription =
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assert(delta != 0)
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result = change(bag.mGetOrPut(key, 0), delta, clamp)
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if result in {cdAbsentToAbsent, cdPresentToAbsent}:
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bag.del(key)
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