LeetCode [706] Design HashMap

706. Design HashMap

Easy

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.

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class MyHashMap { class LinkedNode{ int key, value; LinkedNode next; LinkedNode(int k, int v){ key = k; value = v; next = null; } } int N = 10000; LinkedNode[] buckets = new LinkedNode[N]; /** Initialize your data structure here. */ public MyHashMap() { for(int i=0; i<N; ++i) buckets[i] = new LinkedNode(-1, -1); } /** value will always be non-negative. */ public void put(int key, int value) { LinkedNode prev = findPrev(buckets[key%N], key); if(prev.next==null){ prev.next = new LinkedNode(key, value); }else{ prev.next.value = 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) { LinkedNode prev = findPrev(buckets[key%N], key); if(prev.next==null){ return -1; }else{ return prev.next.value; } } /** Removes the mapping of the specified value key if this map contains a mapping for the key */ public void remove(int key) { LinkedNode prev = findPrev(buckets[key%N], key); if(prev.next == null) return; prev.next = prev.next.next; } LinkedNode findPrev(LinkedNode list, int k){ LinkedNode prev = list, p = list; while(p!=null && p.key!=k){ prev = p; p = p.next; } return prev; } } /** * 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); */