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.
2. Implementation
(1) Array + Double Linked List
class MyHashMap {
final int LEN = 10000;
ListNode[] buckets;
/** Initialize your data structure here. */
public MyHashMap() {
buckets = new ListNode[LEN];
}
/** value will always be non-negative. */
public void put(int key, int value) {
int index = getIndex(key);
if (buckets[index] == null) {
buckets[index] = new ListNode(-1, -1);
}
ListNode preNode = find(buckets[index], key);
if (preNode.next == null) {
preNode.next = new ListNode(key, value);
}
else {
preNode.next.val = 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 = getIndex(key);
if (buckets[index] == null) {
return -1;
}
ListNode preNode = find(buckets[index], key);
if (preNode.next == null) {
return -1;
}
else {
return preNode.next.val;
}
}
/** Removes the mapping of the specified value key if this map contains a mapping for the key */
public void remove(int key) {
int index = getIndex(key);
if (buckets[index] == null) {
return;
}
ListNode preNode = find(buckets[index], key);
if (preNode.next == null) {
return;
}
else {
preNode.next = preNode.next.next;
}
}
class ListNode {
int key, val;
ListNode next;
public ListNode(int key, int value) {
this.key = key;
this.val = value;
next = null;
}
}
public int getIndex(int key) {
return Integer.hashCode(key) % LEN;
}
public ListNode find(ListNode bucket, int key) {
ListNode curNode = bucket;
ListNode preNode = null;
while (curNode != null && curNode.key != key) {
preNode = curNode;
curNode = curNode.next;
}
return preNode;
}
}
/**
* 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);
*/