Add the codes of hashmap (#553)

of chaining and open addressing

codes/python/chapter_hashing/hash_map_chaining.py

@@ -0,0 +1,119 @@
+"""
+File: hash_map_chaining.py
+Created Time: 2023-06-13
+Author: Krahets (krahets@163.com)
+"""
+
+class Pair:
+    """键值对"""
+
+    def __init__(self, key: int, val: str):
+        self.key = key
+        self.val = val
+
+
+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 / 3  # 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:
+        """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
+                return
+
+    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__":
+    # 测试代码
+    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()