706_design_hashmap.md

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]]

Solution

class MyHashMap:

    def __init__(self):
        self.m = {}
        

    def put(self, key: int, value: int) -> None:
        self.m[key] = value
        

    def get(self, key: int) -> int:
        if key in self.m.keys():
            return self.m[key]
        else:
            return -1
        

    def remove(self, key: int) -> None:
        self.m.pop(key, None)
        

if __name__ == '__main__':
    mymap = MyHashMap()
    mymap.put(1, 1)
    mymap.put(2, 2)
    mymap.get(1)
    mymap.get(3)
    mymap.put(2, 1)
    mymap.get(2)
    mymap.remove(2)
    mymap.get(2)