hash function
时间: 2024-01-24 17:03:16 浏览: 33
哈希函数是一种将任意长度的消息压缩到某一固定长度的消息摘要的函数。它将消息作为输入,经过计算后输出一个固定长度的哈希值。哈希函数的主要特点是不可逆和唯一性,即不同的输入消息会产生不同的哈希值,相同的输入消息始终会产生相同的哈希值。哈希函数广泛应用于密码学、数据完整性校验、数据比较等领域。
下面是一个Python中使用哈希函数的例子:
```python
import hashlib
# 创建一个SHA256哈希对象
hash_object = hashlib.sha256()
# 更新哈希对象的消息
hash_object.update(b'Hello, world!')
# 获取哈希值
hex_dig = hash_object.hexdigest()
# 输出哈希值
print(hex_dig) # 输出:b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9
```
相关问题
Calculate hash values for the following keys using the hash function h(k) = k mod 19. 738, 570, 687, 111, 530, 966, 524, 382, 701, 842, 348, 22, 658, 220, 817
To calculate the hash values for the given keys using the hash function `h(k) = k mod 19`, we need to divide each key by 19 and take the remainder.
- `h(738) = 738 mod 19 = 1`
- `h(570) = 570 mod 19 = 7`
- `h(687) = 687 mod 19 = 6`
- `h(111) = 111 mod 19 = 7`
- `h(530) = 530 mod 19 = 15`
- `h(966) = 966 mod 19 = 1`
- `h(524) = 524 mod 19 = 0`
- `h(382) = 382 mod 19 = 1`
- `h(701) = 701 mod 19 = 10`
- `h(842) = 842 mod 19 = 1`
- `h(348) = 348 mod 19 = 6`
- `h(22) = 22 mod 19 = 3`
- `h(658) = 658 mod 19 = 5`
- `h(220) = 220 mod 19 = 9`
- `h(817) = 817 mod 19 = 1`
Therefore, the hash values for the given keys are:
```
738 -> 1
570 -> 7
687 -> 6
111 -> 7
530 -> 15
966 -> 1
524 -> 0
382 -> 1
701 -> 10
842 -> 1
348 -> 6
22 -> 3
658 -> 5
220 -> 9
817 -> 1
```
Implement the hash table (with chaining) data structure. Your table should be able to grow and shrink based on how many items are there. contain at least the following methods: * __init__: initialize the data structure * hash: implement a hash function that is chosen from a universal hash family * search: search for a key in the table, return True if found, False otherwise * insert: insert a key into the table if it is not already in there * delete: delete a key from the table * size: return the number of buckets in your hash table
Sure, here's an implementation of a hash table with chaining in Python:
```python
import random
class HashTable:
def __init__(self, capacity=10):
self.capacity = capacity
self.size = 0
self.table = [[] for _ in range(self.capacity)]
def hash(self, key):
hash_value = 0
for i in range(len(key)):
hash_value = (hash_value * 31 + ord(key[i])) % self.capacity
return hash_value
def search(self, key):
hash_value = self.hash(key)
bucket = self.table[hash_value]
for i in range(len(bucket)):
if bucket[i][0] == key:
return True
return False
def insert(self, key):
if self.search(key):
return
hash_value = self.hash(key)
bucket = self.table[hash_value]
bucket.append((key, None))
self.size += 1
if self.size >= self.capacity * 0.7:
self._resize()
def delete(self, key):
hash_value = self.hash(key)
bucket = self.table[hash_value]
for i in range(len(bucket)):
if bucket[i][0] == key:
bucket.pop(i)
self.size -= 1
if self.size <= self.capacity * 0.3:
self._resize()
return
def size(self):
return self.capacity
def _resize(self):
self.capacity *= 2
new_table = [[] for _ in range(self.capacity)]
for bucket in self.table:
for key, value in bucket:
hash_value = self.hash(key)
new_table[hash_value].append((key, value))
self.table = new_table
```
The `__init__` method initializes the hash table with a specified capacity (default is 10), and creates a list of empty lists to represent the buckets.
The `hash` method takes in a key and maps it to an integer value between 0 and the capacity of the table using a hash function. In this case, we're using a simple polynomial rolling hash function.
The `search` method searches for a key in the table by computing its hash value and checking if it exists in the corresponding bucket.
The `insert` method inserts a key into the table by computing its hash value and appending it to the corresponding bucket. If the load factor of the table exceeds 0.7, the table is resized to double its capacity.
The `delete` method deletes a key from the table by computing its hash value and removing it from the corresponding bucket. If the load factor of the table falls below 0.3, the table is resized to half its capacity.
The `size` method simply returns the current capacity of the table.
The `_resize` method is a private helper method that is called by the `insert` and `delete` methods when the load factor threshold is exceeded. It creates a new table with double or half the capacity of the current table, and rehashes all the keys in the old table into the new table.