Add the codes of hashmap (#553)

of chaining and open addressing

codes/python/chapter_hashing/hash_map_open_addressing.py

@@ -0,0 +1,132 @@
+"""
+File: hash_map_open_addressing.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 HashMapOpenAddressing:
+    """开放寻址哈希表"""
+
+    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: list[Pair | None] = [None] * self.capacity  # 桶数组
+        self.removed = Pair(-1, "-1")  # 删除标记
+
+    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)
+        # 线性探测，从 index 开始向后遍历
+        for i in range(self.capacity):
+            # 计算桶索引，越过尾部返回头部
+            j = (index + i) % self.capacity
+            # 若遇到空桶，说明无此 key ，则返回 None
+            if self.buckets[j] is None:
+                return None
+            # 若遇到指定 key ，则返回对应 val
+            if self.buckets[j].key == key and self.buckets[j] != self.removed:
+                return self.buckets[j].val
+
+    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)
+        # 线性探测，从 index 开始向后遍历
+        for i in range(self.capacity):
+            # 计算桶索引，越过尾部返回头部
+            j = (index + i) % self.capacity
+            # 若遇到空桶、或带有删除标记的桶，则将键值对放入该桶
+            if self.buckets[j] in [None, self.removed]:
+                self.buckets[j] = Pair(key, val)
+                self.size += 1
+                return
+            # 若遇到指定 key ，则更新对应 val
+            if self.buckets[j].key == key:
+                self.buckets[j].val = val
+                return
+
+    def remove(self, key: int):
+        """删除操作"""
+        index = self.hash_func(key)
+        # 线性探测，从 index 开始向后遍历
+        for i in range(self.capacity):
+            # 计算桶索引，越过尾部返回头部
+            j = (index + i) % self.capacity
+            # 若遇到空桶，说明无此 key ，则直接返回
+            if self.buckets[j] is None:
+                return
+            # 若遇到指定 key ，则标记删除并返回
+            if self.buckets[j].key == key:
+                self.buckets[j] = self.removed
+                self.size -= 1
+                return
+
+    def extend(self):
+        """扩容哈希表"""
+        # 暂存原哈希表
+        buckets_tmp = self.buckets
+        # 初始化扩容后的新哈希表
+        self.capacity *= self.extend_ratio
+        self.buckets = [None] * self.capacity
+        self.size = 0
+        # 将键值对从原哈希表搬运至新哈希表
+        for pair in buckets_tmp:
+            if pair not in [None, self.removed]:
+                self.put(pair.key, pair.val)
+
+    def print(self) -> None:
+        """打印哈希表"""
+        for pair in self.buckets:
+            if pair is not None:
+                print(pair.key, "->", pair.val)
+            else:
+                print("None")
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    # 测试代码
+    hashmap = HashMapOpenAddressing()
+
+    # 添加操作
+    # 在哈希表中添加键值对 (key, val)
+    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\nKey -> Value")
+    hashmap.print()
+
+    # 查询操作
+    # 向哈希表输入键 key ，得到值 val
+    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, val)
+    hashmap.remove(16750)
+    print("\n删除 16750 后，哈希表为\nKey -> Value")
+    hashmap.print()