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* Added doctest to skew_heap.py * Update skew_heap.py * Update data_structures/heap/skew_heap.py Co-authored-by: Saptadeep Banerjee <69459134+imSanko@users.noreply.github.com> * Update skew_heap.py * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Update skew_heap.py * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --------- Co-authored-by: Saptadeep Banerjee <69459134+imSanko@users.noreply.github.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
238 lines
5.5 KiB
Python
238 lines
5.5 KiB
Python
#!/usr/bin/env python3
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from __future__ import annotations
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from collections.abc import Iterable, Iterator
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from typing import Any, Generic, TypeVar
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T = TypeVar("T", bound=bool)
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class SkewNode(Generic[T]):
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"""
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One node of the skew heap. Contains the value and references to
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two children.
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"""
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def __init__(self, value: T) -> None:
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self._value: T = value
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self.left: SkewNode[T] | None = None
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self.right: SkewNode[T] | None = None
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@property
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def value(self) -> T:
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"""
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Return the value of the node.
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>>> SkewNode(0).value
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0
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>>> SkewNode(3.14159).value
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3.14159
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>>> SkewNode("hello").value
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'hello'
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>>> SkewNode(None).value
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>>> SkewNode(True).value
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True
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>>> SkewNode([]).value
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[]
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>>> SkewNode({}).value
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{}
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>>> SkewNode(set()).value
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set()
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>>> SkewNode(0.0).value
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0.0
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>>> SkewNode(-1e-10).value
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-1e-10
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>>> SkewNode(10).value
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10
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>>> SkewNode(-10.5).value
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-10.5
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>>> SkewNode().value
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Traceback (most recent call last):
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...
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TypeError: SkewNode.__init__() missing 1 required positional argument: 'value'
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"""
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return self._value
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@staticmethod
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def merge(
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root1: SkewNode[T] | None, root2: SkewNode[T] | None
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) -> SkewNode[T] | None:
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"""
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Merge 2 nodes together.
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>>> SkewNode.merge(SkewNode(10),SkewNode(-10.5)).value
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-10.5
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>>> SkewNode.merge(SkewNode(10),SkewNode(10.5)).value
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10
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>>> SkewNode.merge(SkewNode(10),SkewNode(10)).value
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10
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>>> SkewNode.merge(SkewNode(-100),SkewNode(-10.5)).value
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-100
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"""
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if not root1:
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return root2
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if not root2:
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return root1
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if root1.value > root2.value:
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root1, root2 = root2, root1
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result = root1
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temp = root1.right
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result.right = root1.left
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result.left = SkewNode.merge(temp, root2)
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return result
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class SkewHeap(Generic[T]):
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"""
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A data structure that allows inserting a new value and to pop the smallest
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values. Both operations take O(logN) time where N is the size of the
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structure.
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Wiki: https://en.wikipedia.org/wiki/Skew_heap
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Visualization: https://www.cs.usfca.edu/~galles/visualization/SkewHeap.html
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>>> list(SkewHeap([2, 3, 1, 5, 1, 7]))
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[1, 1, 2, 3, 5, 7]
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>>> sh = SkewHeap()
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>>> sh.pop()
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Traceback (most recent call last):
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...
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IndexError: Can't get top element for the empty heap.
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>>> sh.insert(1)
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>>> sh.insert(-1)
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>>> sh.insert(0)
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>>> list(sh)
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[-1, 0, 1]
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"""
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def __init__(self, data: Iterable[T] | None = ()) -> None:
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"""
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>>> sh = SkewHeap([3, 1, 3, 7])
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>>> list(sh)
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[1, 3, 3, 7]
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"""
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self._root: SkewNode[T] | None = None
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if data:
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for item in data:
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self.insert(item)
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def __bool__(self) -> bool:
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"""
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Check if the heap is not empty.
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>>> sh = SkewHeap()
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>>> bool(sh)
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False
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>>> sh.insert(1)
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>>> bool(sh)
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True
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>>> sh.clear()
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>>> bool(sh)
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False
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"""
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return self._root is not None
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def __iter__(self) -> Iterator[T]:
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"""
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Returns sorted list containing all the values in the heap.
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>>> sh = SkewHeap([3, 1, 3, 7])
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>>> list(sh)
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[1, 3, 3, 7]
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"""
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result: list[Any] = []
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while self:
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result.append(self.pop())
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# Pushing items back to the heap not to clear it.
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for item in result:
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self.insert(item)
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return iter(result)
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def insert(self, value: T) -> None:
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"""
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Insert the value into the heap.
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>>> sh = SkewHeap()
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>>> sh.insert(3)
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>>> sh.insert(1)
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>>> sh.insert(3)
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>>> sh.insert(7)
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>>> list(sh)
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[1, 3, 3, 7]
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"""
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self._root = SkewNode.merge(self._root, SkewNode(value))
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def pop(self) -> T | None:
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"""
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Pop the smallest value from the heap and return it.
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>>> sh = SkewHeap([3, 1, 3, 7])
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>>> sh.pop()
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1
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>>> sh.pop()
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3
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>>> sh.pop()
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3
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>>> sh.pop()
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7
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>>> sh.pop()
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Traceback (most recent call last):
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...
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IndexError: Can't get top element for the empty heap.
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"""
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result = self.top()
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self._root = (
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SkewNode.merge(self._root.left, self._root.right) if self._root else None
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)
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return result
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def top(self) -> T:
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"""
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Return the smallest value from the heap.
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>>> sh = SkewHeap()
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>>> sh.insert(3)
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>>> sh.top()
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3
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>>> sh.insert(1)
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>>> sh.top()
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1
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>>> sh.insert(3)
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>>> sh.top()
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1
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>>> sh.insert(7)
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>>> sh.top()
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1
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"""
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if not self._root:
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raise IndexError("Can't get top element for the empty heap.")
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return self._root.value
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def clear(self) -> None:
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"""
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Clear the heap.
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>>> sh = SkewHeap([3, 1, 3, 7])
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>>> sh.clear()
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>>> sh.pop()
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Traceback (most recent call last):
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...
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IndexError: Can't get top element for the empty heap.
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"""
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self._root = None
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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