0706.Design_HashMap.py

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

Implement the MyHashMap class:

MyHashMap() initializes the object with an empty map.
void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.
 

Example 1:

Input
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]

Explanation
MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1);    // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3);    // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2);    // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2);    // return -1 (i.e., not found), The map is now [[1,1]]
 

Constraints:

0 <= key, value <= 106
At most 104 calls will be made to put, get, and remove.
"""

class ListNode:    #新建class,用于存储 key, value
    def __init__(self, key, value):
        self.key = key
        self.value = value
        self.next = None

class MyHashMap:

    SIZE = 100 #为什么是这个数目，随意填的一个，大一些hash冲突会小一下
    
    def __init__(self):
        #store linked list head in the ListNode(-1, -1)是一个dummy node
        self.map = [ListNode(-1, -1) for _ in range(self.SIZE)]

    def put(self, key: int, value: int) -> None:
        idx = key % self.SIZE
        head = self.map[idx]
        curr = head
        
        while curr.next:
            if curr.next.key == key:
                curr.next.value = value
                break
            curr = curr.next
        
        if not curr.next:
            curr.next = ListNode(key, value)

    def get(self, key: int) -> int:
        idx = key % self.SIZE
        head = self.map[idx]
        curr = head
        
        while curr.next:
            if curr.next.key == key:
                return curr.next.value
            curr = curr.next
        
        return -1

    def remove(self, key: int) -> None:
        idx = key % self.SIZE
        head = self.map[idx]
        curr = head
        while curr.next:
            if curr.next.key == key:
                curr.next = curr.next.next
                break
            curr = curr.next

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