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hash map #12678

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2bee459
Mutable _Item
isidroas Apr 19, 2025
454eded
document falsy item
isidroas Apr 19, 2025
2c99889
resize_down: expected test result
isidroas Apr 19, 2025
6354304
resize_down: actual result
isidroas Apr 19, 2025
875caab
improve comment about falsy item
isidroas Apr 24, 2025
cff17ec
fix long line
isidroas Apr 24, 2025
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27 changes: 23 additions & 4 deletions data_structures/hashing/hash_map.py
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@
VAL = TypeVar("VAL")


@dataclass(frozen=True, slots=True)
@dataclass(slots=True)
class _Item(Generic[KEY, VAL]):
key: KEY
val: VAL
Expand Down Expand Up @@ -72,16 +72,16 @@ def _try_set(self, ind: int, key: KEY, val: VAL) -> bool:

If bucket is empty or key is the same, does insert and return True.

If bucket has another key or deleted placeholder,
that means that we need to check next bucket.
If bucket has another key that means that we need to check next bucket.
"""
stored = self._buckets[ind]
if not stored:
# A falsy item means that is None (bucket never used) or _deleted.
self._buckets[ind] = _Item(key, val)
self._len += 1
return True
elif stored.key == key:
self._buckets[ind] = _Item(key, val)
stored.val = val
return True
else:
return False
Expand Down Expand Up @@ -228,6 +228,25 @@ def __delitem__(self, key: KEY) -> None:
Traceback (most recent call last):
...
KeyError: 4

# Test resize down when sparse
## Setup: resize up
>>> hm = HashMap(100, capacity_factor=0.75)
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Can we go with size 4? In that case, we could avoid the loop.

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Something like this?

# Test resize down when sparse
## Setup: resize up
>>> hm = HashMap(4, capacity_factor=0.75)
>>> len(hm._buckets)
4
>>> hm[0] = 0
>>> hm[1] = 1
>>> hm[2] = 2
>>> len(hm._buckets)
4
>>> hm[3] = 3
>>> len(hm._buckets)
8

## Resize down
>>> del hm[3]
>>> len(hm._buckets)
8
>>> del hm[2]
>>> len(hm._buckets)
4

I've checked that it passes, but I don't know which one I prefer

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I'd prefer to keep tests as linear as possible.

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Let's wait for the 3d opinion.

>>> len(hm._buckets)
100
>>> for i in range(75):
... hm[i] = i
>>> len(hm._buckets)
100
>>> hm[75] = 75
>>> len(hm._buckets)
200

## Resize down
>>> del hm[75]
>>> del hm[74]
>>> len(hm._buckets)
100
"""
for ind in self._iterate_buckets(key):
item = self._buckets[ind]
Expand Down