用 HashTable 继承来实现 DictADT

Author: PegasusWang

docs/8_字典/dict_adt.py

@@ -0,0 +1,180 @@
+# -*- coding: utf-8 -*-
+
+# 从数组和列表章复制的代码
+
+
+class Array(object):
+
+    def __init__(self, size=32):
+        self._size = size
+        self._items = [None] * size
+
+    def __getitem__(self, index):
+        return self._items[index]
+
+    def __setitem__(self, index, value):
+        self._items[index] = value
+
+    def __len__(self):
+        return self._size
+
+    def clear(self, value=None):
+        for i in range(self._items):
+            self._items[i] = value
+
+    def __iter__(self):
+        for item in self._items:
+            yield item
+
+
+class Slot(object):
+    """定义一个 hash 表 数组的槽
+    注意，一个槽有三种状态，看你能否想明白。相比链接法解决冲突，二次探查法删除一个 key 的操作稍微复杂。
+    1.从未使用 HashMap.UNUSED。此槽没有被使用和冲突过，查找时只要找到 UNUSED 就不用再继续探查了
+    2.使用过但是 remove 了，此时是 HashMap.EMPTY，该探查点后边的元素扔可能是有key
+    3.槽正在使用 Slot 节点
+    """
+
+    def __init__(self, key, value):
+        self.key, self.value = key, value
+
+
+class HashTable(object):
+
+    UNUSED = None    # 没被使用过的槽，作为该类变量的一个单例，下边都是is 判断
+    EMPTY = Slot(None, None)     # 使用过但是被删除的槽
+
+    def __init__(self):
+        self._table = Array(7)
+        self.length = 0
+
+    @property
+    def _load_factor(self):
+        # load factor 超过 2/3 就重新分配空间
+        return self.length / float(len(self._table))
+
+    def __len__(self):
+        return self.length
+
+    def _hash1(self, key):
+        """ 计算key的hash值"""
+        return abs(hash(key)) % len(self._table)
+
+    def _find_slot(self, key, for_insert=False):
+        """_find_slot
+
+        :param key:
+        :param for_insert: 是否插入，还是仅仅查询
+        :return:  slot index or None
+        """
+        index = self._hash1(key)
+        base_index = index
+        hash_times = 1
+        _len = len(self._table)
+
+        if not for_insert:  # 查找是否存在 key
+            while self._table[index] is not HashTable.UNUSED:
+                if self._table[index] is HashTable.EMPTY:
+                    index = (index + hash_times * hash_times) % _len    # 一个简单的二次方探查
+                    continue
+                elif self._table[index].key == key:
+                    return index
+                index = (index + hash_times * hash_times) % _len
+                hash_times += 1
+            return None
+        else:
+            while not self._slot_can_insert(index):  # 循环直到找到一个可以插入的槽
+                index = (index + hash_times * hash_times) % _len
+                hash_times += 1
+            return index
+
+    def _slot_can_insert(self, index):
+        return (self._table[index] is HashTable.EMPTY or self._table[index] is HashTable.UNUSED)
+
+    def __contains__(self, key):   # in operator
+        index = self._find_slot(key, for_insert=False)
+        return index is not None
+
+    def add(self, key, value):
+        if key in self:    # key 相同值不一样的时候，用新的值
+            index = self._find_slot(key, for_insert=False)
+            self._table[index].value = value
+            return False
+        else:
+            index = self._find_slot(key, for_insert=True)
+            self._table[index] = Slot(key, value)
+            self.length += 1
+            if self._load_factor >= 0.8:    # 注意超过了 阈值 rehashing
+                self._rehash()
+            return True
+
+    def _rehash(self):
+        old_table = self._table
+        newsize = len(self._table) * 2 + 1   # 扩大 2*n + 1
+        self._table = Array(newsize)
+
+        self.length = 0
+
+        for slot in old_table:
+            if slot is not HashTable.UNUSED and slot is not HashTable.EMPTY:
+                index = self._find_slot(slot.key, for_insert=True)
+                self._table[index] = slot
+                self.length += 1
+
+    def get(self, key, default=None):
+        index = self._find_slot(key, for_insert=False)
+        if index is None:
+            return default
+        else:
+            return self._table[index].value
+
+    def remove(self, key):
+        assert key in self, 'keyerror'
+        index = self._find_slot(key, for_insert=False)
+        value = self._table[index].value
+        self.length -= 1
+        self._table[index] = HashTable.EMPTY
+        return value
+
+    def __iter__(self):
+        for slot in self._table:
+            if slot not in (HashTable.EMPTY, HashTable.UNUSED):
+                yield slot.key   # 和 python dict 一样，默认遍历 key，需要value 的话写个 items() 方法
+
+
+#########################################
+# 上边是从 哈希表章 拷贝过来的代码，我们会直接继承 HashTable 实现 dict
+#########################################
+
+class DictADT(HashTable):
+
+    def _iter_slot(self):
+        for slot in self._table:
+            if slot not in (HashTable.EMPTY, HashTable.UNUSED):
+                yield slot
+
+    def items(self):
+        for slot in self._iter_slot():
+            yield (slot.key, slot.value)
+
+    def keys(self):
+        for slot in self._iter_slot():
+            yield slot.key
+
+    def values(self):
+        for slot in self._iter_slot():
+            yield slot.value
+
+
+def test_dict_adt():
+    import random
+    d = DictADT()
+    l = list(range(30))
+    random.shuffle(l)
+    for i in l:
+        d.add(i, i)
+
+    for i in range(30):
+        assert d.get(i) == i
+
+    assert sorted(list(d.keys())) == sorted(l)