二叉查找树 BinarySearchTree 实现

在二叉查找树里用到了大量的递归调用，首先整清楚一个问题-----引用拷贝，下面代码实际上swap的两个参数都是引用的拷贝。

public class Main {public static void main(String[] args) {String s1 = "1";String s2 = "2";swap(s1,s2);System.out.println(s1);System.out.println(s2);}static void swap(String s1,String s2){String s = s1;s1 = s2;s2 = s;}}

output：

1

2

package changsheng.datastructure;import changsheng.algorithms.util.DuplicateItemException;import changsheng.algorithms.util.EmptyTreeException;import changsheng.algorithms.util.ItemNotFoundException;public class BinarySearchTree<E extends Comparable<? super E>> {private Node<E> root;public BinarySearchTree() {this.root = null;}/** * 清空二叉树 */public void makeEmpty() {this.root = null;}/** * 判断二叉树是否为空 */public boolean isEmpty() {return root == null;}/** * 是否包含元素x */public boolean contains(E x) {return contains(x, root);}private boolean contains(E x, Node<E> r) {int compareResult = x.compareTo(r.value);if (compareResult < 0) {return contains(x, r.left);} else if (compareResult > 0) {return contains(x, r.right);} else {return true;}}/** * 返回二叉树最小值 */public E findMin() {if (isEmpty()) {throw new EmptyTreeException();}return findMin(root).value;}public E find(E x){return elementAt(find(x,root));}/** *返回二叉树最大值  */public E findMax() {if (isEmpty()) {throw new EmptyTreeException();}return findMax(root).value;}/** * 插入x */public void insert(E x) {root = insert(x, root);}/** * 移除x */public void remove(E x) {root = remove(x, root);}/** * 移除最小元素 */public void removeMin(){root = removeMin(root);}/** * 寻找x */private Node<E> find( E x, Node<E> t )    {        while( t != null )        {            if( x.compareTo( t.value ) < 0 )                t = t.left;            else if( x.compareTo( t.value ) > 0 )                t = t.right;            else                return t;    // Match        }                return null;         // Not found    }private E elementAt( Node<E> t )    {        return t == null ? null : t.value;    }private Node<E> findMin(Node<E> r) {if (r != null) {while (r.left != null) {r = r.left;}}return r;}private Node<E> findMax(Node<E> r) {if (r != null) {while (r.right != null) {r = r.right;}}return r;}private Node<E> insert(E x, Node<E> r) {if (r == null) {return new Node<E>(x, null, null);}int compareresult = x.compareTo(r.value);if (compareresult < 0) {r.left = insert(x, r.left);} else if (compareresult > 0) {r.right = insert(x, r.right);} else {throw new DuplicateItemException( x.toString( ) );}return r;}private Node<E> removeMin( Node<E> t )    {        if( t == null )            throw new ItemNotFoundException( );        else if( t.left != null )        {            t.left = removeMin( t.left );            return t;        }        else            return t.right;    }  private Node<E> remove(E x, Node<E> r) {if (r == null) {throw new ItemNotFoundException( x.toString( ) );}int compareResult = x.compareTo(r.value);if (compareResult < 0) {r.left = remove(x,r.left);} else if (compareResult > 0) {r.right = remove(x,r.right);} else if (r.left != null && r.right != null) {r.value = findMin(r.right).value;r.right = removeMin(r.right);} else {r = (r.left != null) ? r.left : r.right;}return r;}private static class Node<E> {Node<E> left;Node<E> right;E value;public Node(E value, Node<E> left, Node<E> right) {this.value = value;this.left = left;this.right = right;}}public static void main( String [ ] args )    {        BinarySearchTree<Integer> t = new BinarySearchTree<Integer>( );        final int NUMS = 4000;        final int GAP  =   37;        System.out.println( "Checking... (no more output means success)" );        for( int i = GAP; i != 0; i = ( i + GAP ) % NUMS )            t.insert( i );        for( int i = 1; i < NUMS; i += 2 )            t.remove( i );        if( t.findMin( ) != 2 || t.findMax( ) != NUMS - 2 )            System.out.println( "FindMin or FindMax error!" );        for( int i = 2; i < NUMS; i += 2 )             if( t.find( i ) != i )                 System.out.println( "Find error1!" );        for( int i = 1; i < NUMS; i += 2 )            if( t.find( i ) != null )                System.out.println( "Find error2!" );    }}