design-hashmap py3

0817_design-hashmap/README.md

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+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`.

0817_design-hashmap/python3/solution.py

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+# Time: O(N / K) ; N is num of all keys and K is num of predefined buckets
+# Space: O(K + M) ; K is num of predefined buckets and M is no. of unique
+#        keys inserted
+
+from collections import deque
+
+class MyHashMap:
+    def __init__(self):
+        # TODO: Better hash function and better initial capacity needed
+        # Maybe initial capacity can even be passed as an option?
+        self.store = [Bucket()] * 997
+
+    def put(self, key: int, value: int) -> None:
+        i = self._hash(key)
+        
+        self.store[i].upsert(key, value)
+
+    def get(self, key: int) -> int:
+        i = self._hash(key)
+        
+        pair = self.store[i].get_pair(key)
+        
+        return pair[1] if pair else -1
+
+    def remove(self, key: int) -> None:
+        i = self._hash(key)
+        return self.store[i].remove(key)
+        
+    def _hash(self, key: int):
+        # TODO: Note down better hash functions
+        return key % 997
+        
+class Bucket:
+    def __init__(self):
+        self.d = deque()
+        
+    def upsert(self, key, value):
+        pair = self.get_pair(key)
+        
+        if pair is not None:
+            pair[1] = value
+        else:
+            self.d.append([key, value])
+        
+    def get_pair(self, key):
+        for item in self.d:
+            if item[0] == key:
+                return item
+    
+    def remove(self, key):
+        item = self.get_pair(key)
+        
+        if item is not None:
+            self.d.remove(item)
+
+
+# Your MyHashMap object will be instantiated and called as such:
+# obj = MyHashMap()
+# obj.put(key,value)
+# param_2 = obj.get(key)
+# obj.remove(key)