Description

Design a HashMap without using any built-in hash table libraries.

To be specific, your design should include these functions:

  • put(key, value) : Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.
  • get(key): Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
  • remove(key) : Remove the mapping for the value key if this map contains the mapping for the key.

Example:

MyHashMap hashMap = new MyHashMap();
hashMap.put(1, 1);          
hashMap.put(2, 2);         
hashMap.get(1);            // returns 1
hashMap.get(3);            // returns -1 (not found)
hashMap.put(2, 1);          // update the existing value
hashMap.get(2);            // returns 1 
hashMap.remove(2);          // remove the mapping for 2
hashMap.get(2);            // returns -1 (not found)

Note:

  • All keys and values will be in the range of [0, 1000000].
  • The number of operations will be in the range of [1, 10000].
  • Please do not use the built-in HashMap library.

分析

题目的意思是：实现散列表法。这道题我参考了一下别人的python实现，首先设置一个质数prime，作为哈希的取模的数，hash数组存放取模后的键值对。put的时候做哈希，存放数据；get的时候也是做哈希，取值；remove的时候，先根据key找到目标键值对，最后删除该键值对就行了。

代码

class MyHashMap:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.prime=20011
        self.hash=[[] for _ in range(self.prime)]
        

    def put(self, key: int, value: int) -> None:
        """
        value will always be non-negative.
        """
        t=key%self.prime
        for item in self.hash[t]:
            if(item[0]==key):
                item[1]=value
                return 
        self.hash[t].append([key,value])
                
        

    def get(self, key: int) -> int:
        """
        Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key
        """
        t=key%self.prime
        for item in self.hash[t]:
            if(item[0]==key):
                return item[1]
        return -1
        

    def remove(self, key: int) -> None:
        """
        Removes the mapping of the specified value key if this map contains a mapping for the key
        """
        t=key%self.prime
        delete=[]
        for item in self.hash[t]:
            if(item[0]==key):
                delete=item
        if(delete):
            self.hash[t].remove(delete)
                

# Your MyHashMap object will be instantiated and called as such:
# obj = MyHashMap()
# obj.put(key,value)
# param_2 = obj.get(key)
# obj.remove(key)

参考文献

​​Python3 详细题解，拉链法实现！​​