映射(Map):
Map 是一種鍵-值對(key-value)集合,Map 集合中的每一個元素都包含一個鍵對象和一個值對象。其中,鍵對象不允許重複,而值對象可以重複,並且值對象還可以是 Map 類型的,就像數組中的元素還可以是數組一樣。
Map接口:
增刪改查
public interface Map<K,V> {
//添加元素
void add(K key,V value);
//刪除元素
V remove(K key);
//是否包含某元素
boolean contains(K key);
//通過鍵獲取值
V get(K key);
//改key對應的value值
void set(K key,V value);
//獲取Map中元素的個數
int getSize();
//Map是否爲空
boolean isEmpty();
}
基於鏈表實現的LinkedListMap:
public class LinkedListMap<K,V> implements Map<K,V> {
private class Node {
public K key;
public V value;
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 = key;
this.value = null;
this.next = null;
}
public Node() {
this.key = null;
this.value = null;
this.next = null;
}
@Override
public String toString(){
return key.toString()+":"+value.toString();
}
}
private Node dummyHead;
private int size;
public LinkedListMap(){
dummyHead = new Node();
size = 0;
}
@Override
public int getSize(){
return size;
}
@Override
public boolean isEmpty(){
return size == 0;
}
//返回key所在的Node
public Node getNode(K key){
Node cur = dummyHead.next;
while (cur != null){
if (cur.key.equals(key)){
return cur;
}
cur = cur.next;
}
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 add(K key,V value){
Node node = getNode(key);
if (node == null){
dummyHead.next = new Node(key,value,dummyHead.next);
size ++;
}else {
//映射中key是唯一的
node.value = value;
}
}
@Override
public void set(K key,V value){
Node node = getNode(key);
if (node == null) {
throw new IllegalArgumentException(key + "does't exist!");
}
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.next != null){
Node delNode = prev.next;
prev.next = delNode.next;
delNode.next = null;
return delNode.value;
}
return null;
}
}
基於二分搜索樹實現的BSTMap:
public class BSTMap<K extends Comparable<K>,V> implements Map<K,V>{
private class Node{
public K key;
public V value;
public Node left,right;
public Node(K key,V value){
this.key = key;
this.value = value;
left = null;
right = null;
}
}
public Node root;
public int size;
public BSTMap(){
root = null;
size = 0;
}
@Override
public int getSize(){
return size;
}
@Override
public boolean isEmpty(){
return size == 0;
}
@Override
public void add(K key,V value){
}
//向以node爲根的二分搜索樹中插入元素(key,value),遞歸算法
//返回插入新節點後二分搜索樹的根
private Node add(Node node,K key,V value){
if(node == null){
size ++;
return new Node(key, value);
}
if (key.compareTo(node.key) < 0){
node.left = add(node.left,key, value);
}else if(key.compareTo(node.key) > 0){ //插入重複元素說明什麼也不做
node.right = add(node.right,key, value);
}else {
node.value = value;
}
return node;
}
//返回以node爲根節點的二分搜索樹中,key所在的節點
private Node getNode(Node node,K key){
if (node == null){
return null;
}
if (key.compareTo(node.key) == 0){
return node;
}else if (key.compareTo(node.key) < 0){
return getNode(node.left,key);
}else { //key.compareTo(node.key) > 0
return getNode(node.right,key);
}
}
@Override
public boolean contains(K key){
return getNode(root,key) != null;
}
@Override
public V get(K key){
Node node = getNode(root,key);
return node == null ? null : node.value;
}
@Override
public void set(K key, V value) {
Node node = getNode(root,key);
if (node == null){
throw new IllegalArgumentException(key + "dose't exist!");
}
node.value = value;
}
//返回以node爲根的二分搜索樹的最小值所在的節點,遞歸算法
private Node minimum(Node node){
if (node.left == null){
return node;
}
return minimum(node.left);
}
//刪除以node爲根的二分搜索樹的最小節點
//返回刪除節點後新的二分搜索樹的根
private Node removeMin(Node node){
if (node.left == null){
Node rightNode = node.right;
node.right = null;
size --;
return rightNode;
}
node.left = removeMin(node.left);
return node;
}
@Override
public V remove(K key){
Node node = getNode(root,key);
if (node != null){
root = remove(root,key);
return node.value;
}
return null;
}
//刪除掉以node爲根的二分搜索樹中值爲e節點,遞歸算法
//返回刪除節點後新的二分搜索樹的根
private Node remove(Node node,K key){
if (node == null){
return null;
}
if (key.compareTo(node.key) < 0){
node.left = remove(node.left,key);
return node;
}else if (key.compareTo(node.key) > 0){
node.right = remove(node.right,key);
return node;
}
else { //key == node.key
//待刪除節點左子樹爲空的情況
if (node.left == null){
Node rightNode = node.right;
node.right = null;
size --;
return rightNode;
}
//待刪除節點右子樹爲空的情況
if (node.right == null){
Node leftNode = node.left;
node.left = null;
size --;
return leftNode;
}
//待刪除節點均不爲空的情況
//找到比待刪除節點大的最小節點,即待刪除節點右子樹的最小節點(後繼節點)。
//或找到比待刪除節點小的最大節點,即待刪除節點左子樹的最大節點(前驅節點)
//用這個節點頂替待刪除節點的位置
Node successor = minimum(node.right);
successor.right = removeMin(node.right);
successor.left = node.left;
node.left = null;
node.right = null;
return successor;
}
}
}
一般來說,BSTMap對數據操作時其性能是遠高於LinkedListMap的,因爲BSTMap增刪改查的方法時間複雜度是O(logn)的,而LinkedListMap是O(n)的。