706. Design HashMap

📋 Đề Bài

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.

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)Linked List (Danh sách liên kết)

⏱️ Thời gian O(n)

💾 Không gian O(n)

💻 Lời Giải

Python 0706-design-hashmap.py

class ListNode:
    def __init__(self, key: int, value: int):
        self.key = key
        self.value = value
        self.next = None

class MyHashMap:

    def __init__(self):
        self.constMaxN = 19997
        self.contains = [None for _ in range(self.constMaxN)]
        
    def hashing(self, key: int) -> int:
        return key % self.constMaxN

    def put(self, key: int, value: int) -> None:
        self.remove(key)
        h = self.hashing(key)
        
        if self.contains[h] == None:
            self.contains[h] = ListNode(key, value)
        else:
            head = self.contains[h]
            newNode = ListNode(key, value)
            newNode.next = head
            self.contains[h] = newNode

    def get(self, key: int) -> int:
        h = self.hashing(key)
        currNode = self.contains[h]
        while currNode:
            if currNode.key == key:
                return currNode.value
            currNode = currNode.next
        return -1

    def remove(self, key: int) -> None:
        h = self.hashing(key)
        head = self.contains[h]
        
        if head == None:
            return
        
        if head.key == key:
            self.contains[h] = head.next
            return
        currNode = head
        
        while currNode.next:
            if currNode.next.key == key:
                currNode.next = currNode.next.next
                return
            currNode = currNode.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)