LinkedListMap.java

package will.zhang.map;

/**
 * 基于链表实现的映射(Map)
 *
 * 时间复杂度分析
 * 增
 * add(K, V)    O(n)
 * 删
 * remove(K)    O(n)
 * 改
 * set(K, V)    O(n)
 * 查
 * get(K)       O(n)
 * contains(K)  O(n)
 * @param <K>
 * @param <V>
 */
public class LinkedListMap<K, V> implements Map<K, V> {

    //还是有一个虚拟的头指针
    private Node dummyHead;
    private int size;

    public LinkedListMap(){
        dummyHead = new Node();
        size = 0;
    }

    @Override
    public void add(K key, V value) {
        Node node = getNode(key);
        if(node == null){
            dummyHead.next = new Node(key, value, dummyHead.next);
            size++;
        }else{
            //这里取决于设计, 如果遇到已经存在于的key, 可以选择更新或者报错等等
            node.value = value;
        }
    }

    @Override
    public V remove(K key) {
        Node prev = dummyHead;
        while(prev.next != null){
            if(prev.next.key.equals(key)){
                break;
            }
            prev = prev.next;
        }

        if(prev != null){
            Node delNode = prev.next;
            prev.next = delNode.next;
            delNode.next = null;
            size--;
            return delNode.value;
        }
        return null;
    }

    @Override
    public boolean contains(K key) {
        return getNode(key) != null;
    }

    @Override
    public V get(K key) {
        Node node = getNode(key);
        return node == null ? null : node.value;
    }

    @Override
    public void set(K key, V newValue) {
        Node node = getNode(key);
        if(node == null){
            throw new IllegalArgumentException(key + " doesn't exist");
        }
        node.value = newValue;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * 返回key所属的节点
     * @param key
     * @return
     */
    private Node getNode(K key){
        Node cur = dummyHead.next;
        while(cur != null){
            if(cur.key.equals(key)){
                return cur;
            }
            cur = cur.next;
        }
        return null;
    }

    /**
     * 节点
     * 链表的内部类
     */
    private class Node {
        //这里跟以前实现的链表不同的是, 以前只有一个E用来存放单个元素
        //这里用了K key和V value分别存放映射的键和值
        public K key;
        public V value;
        //下一个节点
        public Node next;

        public Node(K key, V value, Node next){
            this.key = key;
            this.value = value;
            this.next = next;
        }

        public Node(K key){
            this(key, null, null);
        }

        public Node(){
            this(null, null, null);
        }

        @Override
        public String toString() {
            return key.toString() + " : " + value.toString();
        }
    }
}