# 706. Design HashMap

###### tags: `leetcode`,`structure`,`easy`

>ref: https://leetcode.com/problems/design-hashmap/
>
Design a HashMap without using any built-in hash table libraries.

Implement the MyHashMap class:

* MyHashMap() initializes the object with an empty map.
* void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
* int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
* void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.

>Example 1:
Input
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]


>1. 越大listnode[] 查找key時間越短 (空間換取時間)
>2. 查找到目標前一個listnode或尾端

class MyHashMap {
    
    final int size=10000;
    
    ListNode[] list;

    public MyHashMap() {
        list= new ListNode[size];
    }
    
    public void put(int key, int value) {
        
        int bucket= hash(key);
        
        //find key in bucket 
        ListNode pre=find(bucket,key);
     
        //replace or create
        if(pre.next!=null){
            //find exist key
            pre.next.value=value;
        }else{
            //no exist key
            pre.next=new ListNode(key,value);
        }
    }
    
    public int get(int key) {
        
        int bucket= hash(key);
        
        //find key in bucket 
        ListNode pre=find(bucket,key);
     
        if(pre.next!=null){
            //find
            return pre.next.value;
        }else{
            //to end no find
            return -1; 
        }
    }
    
    public void remove(int key) {
        int bucket= hash(key);
        
        //find key in bucket 
        ListNode pre=find(bucket,key);
     
        //remove
        if(pre.next!=null){
            pre.next=pre.next.next;
        }
    }
    
    private int hash(int key){
        return key%list.length;
    }
    
    private ListNode find(int bucket,int key){
        
        //init bucket 
        if(list[bucket]==null){
            list[bucket]=new ListNode(-1,-1);
        }
        
        ListNode cur=list[bucket];
        
        while(cur.next!=null && cur.next.key!=key){
            cur=cur.next;
        }
        return cur;
    }
    
    class ListNode{
        int key;
        int value;
        ListNode next;
        
        ListNode(int key,int value){
            this.key=key;
            this.value=value;
        }
    }    
}