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* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
119 lines
3.8 KiB
Python
119 lines
3.8 KiB
Python
"""
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File: hash_map_chaining.py
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Created Time: 2023-06-13
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Author: krahets (krahets@163.com)
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"""
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import sys
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from pathlib import Path
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sys.path.append(str(Path(__file__).parent.parent))
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from chapter_hashing.array_hash_map import Pair
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class HashMapChaining:
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"""Hash table with separate chaining"""
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def __init__(self):
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"""Constructor"""
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self.size = 0 # Number of key-value pairs
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self.capacity = 4 # Hash table capacity
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self.load_thres = 2.0 / 3.0 # Load factor threshold that triggers capacity growth
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self.extend_ratio = 2 # Capacity growth factor
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self.buckets = [[] for _ in range(self.capacity)] # Bucket array
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def hash_func(self, key: int) -> int:
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"""Hash function"""
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return key % self.capacity
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def load_factor(self) -> float:
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"""Load factor"""
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return self.size / self.capacity
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def get(self, key: int) -> str | None:
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"""Lookup operation"""
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index = self.hash_func(key)
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bucket = self.buckets[index]
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# Traverse the bucket; if key is found, return its corresponding val
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for pair in bucket:
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if pair.key == key:
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return pair.val
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# Return None if key is not found
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return None
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def put(self, key: int, val: str):
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"""Insert operation"""
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# Grow the capacity when the load factor exceeds the threshold
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if self.load_factor() > self.load_thres:
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self.extend()
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index = self.hash_func(key)
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bucket = self.buckets[index]
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# Traverse the bucket; if the specified key is found, update its val and return
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for pair in bucket:
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if pair.key == key:
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pair.val = val
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return
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# If key is absent, append the key-value pair at the end
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pair = Pair(key, val)
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bucket.append(pair)
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self.size += 1
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def remove(self, key: int):
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"""Remove operation"""
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index = self.hash_func(key)
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bucket = self.buckets[index]
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# Traverse the bucket and remove the key-value pair
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for pair in bucket:
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if pair.key == key:
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bucket.remove(pair)
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self.size -= 1
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break
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def extend(self):
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"""Grow the hash table capacity"""
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# Keep a reference to the original hash table
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buckets = self.buckets
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# Initialize a new hash table with the expanded capacity
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self.capacity *= self.extend_ratio
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self.buckets = [[] for _ in range(self.capacity)]
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self.size = 0
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# Move the key-value pairs from the original hash table to the new one
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for bucket in buckets:
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for pair in bucket:
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self.put(pair.key, pair.val)
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def print(self):
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"""Print the hash table"""
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for bucket in self.buckets:
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res = []
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for pair in bucket:
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res.append(str(pair.key) + " -> " + pair.val)
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print(res)
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"""Driver code"""
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if __name__ == "__main__":
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# Initialize the hash table
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hashmap = HashMapChaining()
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# Insert operation
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# Insert the key-value pair (key, value) into the hash table
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hashmap.put(12836, "小哈")
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hashmap.put(15937, "小啰")
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hashmap.put(16750, "小算")
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hashmap.put(13276, "小法")
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hashmap.put(10583, "小鸭")
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print("\nHash table after insertion:\n[Key1 -> Value1, Key2 -> Value2, ...]")
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hashmap.print()
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# Lookup operation
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# Look up key in the hash table to obtain value
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name = hashmap.get(13276)
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print("\nLook up student ID 13276 to obtain the name " + name)
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# Remove operation
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# Remove the key-value pair (key, value) from the hash table
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hashmap.remove(12836)
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print("\nHash table after removing 12836:\n[Key1 -> Value1, Key2 -> Value2, ...]")
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hashmap.print()
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