Problem description:

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.

Solution:

Array with list of Node to handle collision

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class ListNode:
    def __init__(self, key, val):
        self.pair = (key, val)
        self.next = None
        

class MyHashMap:

    def __init__(self):
        self.size = 1000
        self.hash = [None]* self.size
        

    def put(self, key: int, value: int) -> None:
        index = key % self.size
        if self.hash[index] == None:
            # not in map yet
            self.hash[index] = ListNode(key, value)
        else:
            cur = self.hash[index]
            while True:
                if cur.pair[0] == key:
                    cur.pair = (key, value)
                    return
                if cur.next == None:
                    break
                cur = cur.next
            cur.next = ListNode(key, value)

    def get(self, key: int) -> int:
        index = key % self.size
        
        if self.hash[index] == None:
            return -1
        else:
            cur = self.hash[index]
            while True:
                if cur.pair[0] == key:
                    return cur.pair[1]
                if cur.next == None:
                    return -1
                cur = cur.next

    def remove(self, key: int) -> None:
        index = key % self.size
        cur = pre = self.hash[index]
        if not cur: return
        if cur.pair[0] == key:
            self.hash[index] = self.hash[index].next
        else:
            cur = cur.next
            while cur:
                if cur.pair[0] == key:
                    pre.next = cur.next
                    break
                else:
                    cur, pre = cur.next, pre.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)

time complexity: $O()$
space complexity: $O()$
reference:
related problem: