91 lines
2.8 KiB
Python
91 lines
2.8 KiB
Python
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"""
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An implementation of skip list.
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The list stores positive integers without duplicates.
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跳表的一种实现方法。
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跳表中储存的是正整数，并且储存的是不重复的。
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Author: Wenru
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"""
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from typing import Optional
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import random
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class ListNode:
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def __init__(self, data: Optional[int] = None):
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self._data = data
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self._forwards = [] # Forward pointers
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class SkipList:
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_MAX_LEVEL = 16
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def __init__(self):
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self._level_count = 1
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self._head = ListNode()
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self._head._forwards = [None] * type(self)._MAX_LEVEL
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def find(self, value: int) -> Optional[ListNode]:
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p = self._head
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for i in range(self._level_count - 1, -1, -1): # Move down a level
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while p._forwards[i] and p._forwards[i]._data < value:
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p = p._forwards[i] # Move along level
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return p._forwards[0] if p._forwards[0] and p._forwards[0]._data == value else None
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def insert(self, value: int):
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level = self._random_level()
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if self._level_count < level: self._level_count = level
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new_node = ListNode(value)
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new_node._forwards = [None] * level
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update = [self._head] * level # update is like a list of prevs
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p = self._head
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for i in range(level - 1, -1, -1):
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while p._forwards[i] and p._forwards[i]._data < value:
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p = p._forwards[i]
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update[i] = p # Found a prev
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for i in range(level):
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new_node._forwards[i] = update[i]._forwards[i] # new_node.next = prev.next
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update[i]._forwards[i] = new_node # prev.next = new_node
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def delete(self, value):
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update = [None] * self._level_count
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p = self._head
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for i in range(self._level_count - 1, -1, -1):
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while p._forwards[i] and p._forwards[i]._data < value:
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p = p._forwards[i]
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update[i] = p
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if p._forwards[0] and p._forwards[0]._data == value:
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for i in range(self._level_count - 1, -1, -1):
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if update[i]._forwards[i] and update[i]._forwards[i]._data == value:
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update[i]._forwards[i] = update[i]._forwards[i]._forwards[i] # Similar to prev.next = prev.next.next
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def _random_level(self, p: float = 0.5) -> int:
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level = 1
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while random.random() < p and level < type(self)._MAX_LEVEL:
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level += 1
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return level
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def __repr__(self) -> str:
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values = []
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p = self._head
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while p._forwards[0]:
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values.append(str(p._forwards[0]._data))
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p = p._forwards[0]
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return "->".join(values)
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if __name__ == "__main__":
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l = SkipList()
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for i in range(10):
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l.insert(i)
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print(l)
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p = l.find(7)
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print(p._data)
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l.delete(3)
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print(l)
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