Tags: "leetcode", "hashmap", "ood", access_time 2-min read

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Design Hashmap

Created: March 29, 2020 by [lek-tin]

Last updated: March 29, 2020

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

To be specific, your design should include these functions:

  1. put(key, value): Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.
  2. get(key): Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
  3. 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

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

Solution

class Node:
    def __init__(self, _key=None, _val=None, _next=None):
        self.key = _key
        self.val = _val
        self.next = _next

class Bucket:
    def __init__(self):
        self.head = Node()

    def display(self):
        curr = self.head
        while curr:
            print(curr.val)
            curr = curr.next

    def deleteByKey(self, key):
        curr = self.head

        while curr and curr.next:
            if curr.next.key == key:
                curr.next = curr.next.next
                return
            curr = curr.next

    def getByKey(self, key):
        curr = self.head.next
        while curr:
            if curr.key == key:
                return curr
            curr = curr.next

        return None

    def updateByKey(self, key, val):
        node = self.getByKey(key)
        if node:
            node.val = val
        else:
            self.head.next = Node(key, val, self.head.next)

class MyHashMap:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.keyRange = 769
        self.buckets = [Bucket() for i in range(self.keyRange)]

    def _hash(self, key):
        return key % self.keyRange

    def put(self, key: int, value: int) -> None:
        """
        value will always be non-negative.
        """
        bucketIndex = self._hash(key)
        self.buckets[bucketIndex].updateByKey(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
        """
        bucketIndex = self._hash(key)
        node = self.buckets[bucketIndex].getByKey(key)
        return node.val if node != None else -1

    def remove(self, key: int) -> None:
        """
        Removes the mapping of the specified value key if this map contains a mapping for the key
        """
        bucketIndex = self._hash(key)
        self.buckets[bucketIndex].deleteByKey(key)

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