用BST实现HashMap
把核心的逻辑都放在Node里面
所以Node的代码是:
1 public class MapNode<K extends Comparable<K>, V> { 2 private K key; 3 private V value; 4 private MapNode<K, V> left; 5 private MapNode<K, V> right; 6 7 public MapNode(K key, V value) { 8 this.key = key; 9 this.value = value; 10 } 11 12 public V put(K key, V value) { 13 if(this.key.compareTo(key) == 0) { 14 V oldValue = this.value; 15 this.value = value; 16 return oldValue; 17 } else if(this.key.compareTo(key) < 0) { 18 if(right == null) { 19 right = new MapNode(key, value); 20 return null; 21 } else { 22 return right.put(key, value); 23 } 24 } else { 25 if(left == null) { 26 left = new MapNode(key, value); 27 return null; 28 } else { 29 return left.put(key, value); 30 } 31 } 32 } 33 34 public V get(K key) { 35 if(this.key.compareTo(key) == 0) { 36 return this.value; 37 } else if(this.key.compareTo(key) < 0) { 38 return right == null? null: right.get(key); 39 } else { 40 return left == null? null: left.get(key); 41 } 42 } 43 }
Map部分的代码是:
1 public class ImplementHashmapUsingBST<K extends Comparable<K>, V> { 2 MapNode<K, V> root; 3 int size; 4 5 public ImplementHashmapUsingBST() { 6 size = 0; 7 } 8 9 public V get(K key) { 10 if(root == null) { 11 return null; 12 } 13 return root.get(key); 14 } 15 16 public V put(K key, V value) { 17 if(root == null){ 18 root = new MapNode(key, value); 19 return null; 20 } else { 21 V oldValue = root.put(key, value); 22 if(oldValue == null) { 23 size++; 24 return null; 25 } 26 return oldValue; 27 } 28 } 29 30 public static void main(String[] args) { 31 ImplementHashmapUsingBST<String, String> sample = new ImplementHashmapUsingBST(); 32 sample.put("Apple", "Fruit"); 33 sample.put("Pork", "Meat"); 34 System.out.println(sample.get("Apple")); 35 } 36 37 }