[LeetCode] 706. Design HashMap
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 1hashMap.get(3); // returns -1 (not found)hashMap.put(2, 1); // update the existing valuehashMap.get(2); // returns 1 hashMap.remove(2); // remove the mapping for 2hashMap.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
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); */