LeetCode 706. Design HashMap

Description

https://leetcode.com/problems/design-hashmap/

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 putget, and remove.

Follow up: Please do not use the built-in HashMap library.

Explanation

A simple way is to create a big array. The indices of array are keys, values are corresponding values.

Python Solution

class MyHashMap:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.keys = [-1 for _ in range(1000000)]
        
            
        
    def put(self, key: int, value: int) -> None:
        """
        value will always be non-negative.
        """                
        if key >= len(self.keys):
            for _ in range(1000000):
                self.keys.append(-1)
        
        self.keys[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
        """
        return self.keys[key]

                
            
    def remove(self, key: int) -> None:
        """
        Removes the mapping of the specified value key if this map contains a mapping for the key
        """
        self.keys[key] = -1
        
        
        


# 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(N).
  • Space Complexity: O(N).

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