Problem
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.
</>复制代码
class MyHashMap {
class ListNode {
ListNode next;
int key, val;
ListNode(int key, int value) {
this.key = key;
this.val = value;
}
}
class Bucket {
final ListNode head = new ListNode(-1, -1);
}
final int size = 10000;
final Bucket[] buckets = new Bucket[size];
/** Initialize your data structure here. */
public MyHashMap() {
}
//used to find the bucket
private int hash(int key) {
return key % size;
}
//used to find node by key in certain bucket
private ListNode findNode(Bucket bucket, int key) {
ListNode head = bucket.head;
ListNode node = head;
while (head != null && head.key != key) {
//when head == null, or head.key == key, return its previous node
node = head;
head = head.next;
}
return node;
}
/** value will always be non-negative. */
public void put(int key, int value) {
int i = hash(key);
if (buckets[i] == null) buckets[i] = new Bucket();
ListNode pre = findNode(buckets[i], key);
if (pre.next == null) {
pre.next = new ListNode(key, value);
} else {
pre.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 i = hash(key);
if (buckets[i] == null) return -1;
ListNode pre = findNode(buckets[i], key);
if (pre.next == null) {
return -1;
} else {
return pre.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 i = hash(key);
if (buckets[i] == null) return;
ListNode pre = findNode(buckets[i], key);
if (pre.next == null) return;
else pre.next = pre.next.next;
}
}
/**
* 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);
*/
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