## DEV Community

Abhishek Chaudhary

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# 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 put, get, and remove.

SOLUTION:

class MyHashMap:

def __init__(self):
self.size = 107
self.arr = [[] for i in range(self.size)]

def hfn(self, key):
key = ((key >> 16) ^ key) * 0x45d9f3b
key = ((key >> 16) ^ key) * 0x45d9f3b
key = (key >> 16) ^ key
return key % self.size

def put(self, key: int, value: int) -> None:
self.remove(key)
self.arr[self.hfn(key)].append((key, value))

def get(self, key: int) -> int:
curr = self.arr[self.hfn(key)]
val = -1
for k, v in curr:
if k == key:
val = v
break
return val

def remove(self, key: int) -> None:
k = len(self.arr[self.hfn(key)])
for i in range(k):
if self.arr[self.hfn(key)][i][0] == key:
self.arr[self.hfn(key)][i] = self.arr[self.hfn(key)][-1]
self.arr[self.hfn(key)].pop()
break

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