78 lines
2.1 KiB
Python
78 lines
2.1 KiB
Python
"""
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Generate a table of unique items.
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The `UniqueTable` class collects items into an array, removing duplicates. Each
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item is mapped to its offset in the final array.
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This is a compression technique for compile-time generated tables.
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"""
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try:
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from typing import Any, List, Dict, Tuple, Sequence # noqa
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except ImportError:
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pass
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class UniqueTable:
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"""
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Collect items into the `table` list, removing duplicates.
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"""
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def __init__(self):
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# type: () -> None
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# List of items added in order.
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self.table = list() # type: List[Any]
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# Map item -> index.
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self.index = dict() # type: Dict[Any, int]
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def add(self, item):
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# type: (Any) -> int
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"""
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Add a single item to the table if it isn't already there.
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Return the offset into `self.table` of the item.
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"""
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if item in self.index:
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return self.index[item]
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idx = len(self.table)
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self.index[item] = idx
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self.table.append(item)
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return idx
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class UniqueSeqTable:
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"""
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Collect sequences into the `table` list, removing duplicates.
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Sequences don't have to be of the same length.
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"""
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def __init__(self):
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# type: () -> None
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self.table = list() # type: List[Any]
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# Map seq -> index.
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self.index = dict() # type: Dict[Tuple[Any, ...], int]
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def add(self, seq):
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# type: (Sequence[Any]) -> int
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"""
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Add a sequence of items to the table. If the table already contains the
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items in `seq` in the same order, use those instead.
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Return the offset into `self.table` of the beginning of `seq`.
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"""
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if len(seq) == 0:
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return 0
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seq = tuple(seq)
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if seq in self.index:
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return self.index[seq]
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idx = len(self.table)
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self.table.extend(seq)
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# Add seq and all sub-sequences to `index`.
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for length in range(1, len(seq) + 1):
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for offset in range(len(seq) - length + 1):
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self.index[seq[offset:offset+length]] = idx + offset
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return idx
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