Design a HashMap without using any built-in hash table libraries.
To be specific, your design should include these functions:
put(key, value) : Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.
get(key): Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
remove(key) : Remove the mapping for the value key if this map contains the mapping for the key.
Example:
MyHashMap hashMap = new MyHashMap();
hashMap.put(1, 1);
hashMap.put(2, 2);
hashMap.get(1); // returns 1
hashMap.get(3); // returns -1 (not found)
hashMap.put(2, 1); // update the existing value
hashMap.get(2); // returns 1
hashMap.remove(2); // remove the mapping for 2
hashMap.get(2); // returns -1 (not found)
Note:
All keys and values will be in the range of [0, 1000000].
The number of operations will be in the range of [1, 10000].
Please do not use the built-in HashMap library.
Solution:
import java.util.AbstractMap;
class MyHashMap { private List<Map.Entry<Integer, Integer>>[] map; private int size = 10001;
/** Initialize your data structure here. */ public MyHashMap() { map = new ArrayList[size]; }
/** value will always be non-negative. */ public void put(int key, int value) { int index = key % size; if (map[index] == null) { map[index] = new ArrayList<>(); } map[index].removeIf(e -> e.getKey().equals(key)); map[index].add(new AbstractMap.SimpleEntry(key, value)); }
/** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */ public int get(int key) { int index = key % size; if (map[index] == null) { return -1; } for (Map.Entry<Integer, Integer> entry : map[index]) { if (entry.getKey() == key) { return entry.getValue(); } } return -1; }
/** Removes the mapping of the specified value key if this map contains a mapping for the key */ public void remove(int key) { int index = key % size; if (map[index] == null) { return; } map[index].removeIf(e -> e.getKey().equals(key)); } }
/** * Your MyHashMap object will be instantiated and called as such: * MyHashMap obj = new MyHashMap(); * obj.put(key,value); * int param_2 = obj.get(key); * obj.remove(key); */