hello-algo/codes/python/chapter_hashing/hash_map_chaining.py

"""
File: hash_map_chaining.py
Created Time: 2023-06-13
Author: Krahets (krahets@163.com)
"""

import sys
from pathlib import Path

sys.path.append(str(Path(__file__).parent.parent))
from chapter_hashing.array_hash_map import Pair


class HashMapChaining:
    """链式地址哈希表"""

    def __init__(self):
        """构造方法"""
        self.size = 0  # 键值对数量
        self.capacity = 4  # 哈希表容量
        self.load_thres = 2.0 / 3.0  # 触发扩容的负载因子阈值
        self.extend_ratio = 2  # 扩容倍数
        self.buckets = [[] for _ in range(self.capacity)]  # 桶数组

    def hash_func(self, key: int) -> int:
        """哈希函数"""
        return key % self.capacity

    def load_factor(self) -> float:
        """负载因子"""
        return self.size / self.capacity

    def get(self, key: int) -> str | None:
        """查询操作"""
        index = self.hash_func(key)
        bucket = self.buckets[index]
        # 遍历桶，若找到 key 则返回对应 val
        for pair in bucket:
            if pair.key == key:
                return pair.val
        # 若未找到 key 则返回 None
        return None

    def put(self, key: int, val: str):
        """添加操作"""
        # 当负载因子超过阈值时，执行扩容
        if self.load_factor() > self.load_thres:
            self.extend()
        index = self.hash_func(key)
        bucket = self.buckets[index]
        # 遍历桶，若遇到指定 key ，则更新对应 val 并返回
        for pair in bucket:
            if pair.key == key:
                pair.val = val
                return
        # 若无该 key ，则将键值对添加至尾部
        pair = Pair(key, val)
        bucket.append(pair)
        self.size += 1

    def remove(self, key: int):
        """删除操作"""
        index = self.hash_func(key)
        bucket = self.buckets[index]
        # 遍历桶，从中删除键值对
        for pair in bucket:
            if pair.key == key:
                bucket.remove(pair)
                self.size -= 1
                break

    def extend(self):
        """扩容哈希表"""
        # 暂存原哈希表
        buckets = self.buckets
        # 初始化扩容后的新哈希表
        self.capacity *= self.extend_ratio
        self.buckets = [[] for _ in range(self.capacity)]
        self.size = 0
        # 将键值对从原哈希表搬运至新哈希表
        for bucket in buckets:
            for pair in bucket:
                self.put(pair.key, pair.val)

    def print(self):
        """打印哈希表"""
        for bucket in self.buckets:
            res = []
            for pair in bucket:
                res.append(str(pair.key) + " -> " + pair.val)
            print(res)


"""Driver Code"""
if __name__ == "__main__":
    # 初始化哈希表
    hashmap = HashMapChaining()

    # 添加操作
    # 在哈希表中添加键值对 (key, value)
    hashmap.put(12836, "小哈")
    hashmap.put(15937, "小啰")
    hashmap.put(16750, "小算")
    hashmap.put(13276, "小法")
    hashmap.put(10583, "小鸭")
    print("\n添加完成后，哈希表为\n[Key1 -> Value1, Key2 -> Value2, ...]")
    hashmap.print()

    # 查询操作
    # 向哈希表输入键 key ，得到值 value
    name = hashmap.get(13276)
    print("\n输入学号 13276 ，查询到姓名 " + name)

    # 删除操作
    # 在哈希表中删除键值对 (key, value)
    hashmap.remove(12836)
    print("\n删除 12836 后，哈希表为\n[Key1 -> Value1, Key2 -> Value2, ...]")
    hashmap.print()