二叉树

/** 二叉树节点 */
public class BTNode {
private char key;
private BTNode left, right;

public BTNode( char key) {
this (key, null , null );
}

public BTNode( char key, BTNode left, BTNode right) {
this .key = key;
this .left = left;
this .right = right;
}

public char getKey() {
return key;
}

public void setKey( char key) {
this .key = key;
}

public BTNode getLeft() {
return left;
}

public void setLeft(BTNode left) {
this .left = left;
}

public BTNode getRight() {
return right;
}

public void setRight(BTNode right) {
this .right = right;
}
}

遍历二叉树

/** 二叉树遍历 */
public class BinTree {
protected BTNode root;

public BinTree(BTNode root) {
this .root = root;
}

public BTNode getRoot() {
return root;
}

/** 构造树 */
public static BTNode init() {
BTNode a = new BTNode('A');
BTNode b = new BTNode('B', null , a);
BTNode c = new BTNode('C');
BTNode d = new BTNode('D', b, c);
BTNode e = new BTNode('E');
BTNode f = new BTNode('F', e, null );
BTNode g = new BTNode('G', null , f);
BTNode h = new BTNode('H', d, g);
return h; // root
}

/** 访问节点 */
public static void visit(BTNode p) {
System.out.print(p.getKey() + " " );
}

/** 递归实现前序遍历 */
protected static void preorder(BTNode p) {
if (p != null ) {
visit(p);
preorder(p.getLeft());
preorder(p.getRight());
}
}

/** 递归实现中序遍历 */
protected static void inorder(BTNode p) {
if (p != null ) {
inorder(p.getLeft());
visit(p);
inorder(p.getRight());
}
}

/** 递归实现后序遍历 */
protected static void postorder(BTNode p) {
if (p != null ) {
postorder(p.getLeft());
postorder(p.getRight());
visit(p);
}
}

/** 非递归实现前序遍历 */
protected static void iterativePreorder(BTNode p) {
Stack<BTNode> stack = new Stack<BTNode>();
if (p != null ) {
stack.push(p);
while (!stack.empty()) {
p = stack.pop();
visit(p);
if (p.getRight() != null )
stack.push(p.getRight());
if (p.getLeft() != null )
stack.push(p.getLeft());
}
}
}

/** 非递归实现后序遍历 */
protected static void iterativePostorder(BTNode p) {
BTNode q = p;
Stack<BTNode> stack = new Stack<BTNode>();
while (p != null ) {
// 左子树入栈
for (; p.getLeft() != null ; p = p.getLeft())
stack.push(p);
// 当前节点无右子或右子已经输出
while (p != null && (p.getRight() == null || p.getRight() == q)) {
visit(p);
q = p; // 记录上一个已输出节点
if (stack.empty())
return ;
p = stack.pop();
}
// 处理右子
stack.push(p);
p = p.getRight();
}
}

/** 非递归实现中序遍历 */
protected static void iterativeInorder(BTNode p) {
Stack<BTNode> stack = new Stack<BTNode>();
while (p != null ) {
while (p != null ) {
if (p.getRight() != null )
stack.push(p.getRight()); // 当前节点右子入栈
stack.push(p); // 当前节点入栈
p = p.getLeft();
}
p = stack.pop();
while (!stack.empty() && p.getRight() == null ) {
visit(p);
p = stack.pop();
}
visit(p);
if (!stack.empty())
p = stack.pop();
else
p = null ;
}
}

public static void main(String[] args) {
BinTree tree = new BinTree(init());
System.out.print( " Pre-Order:" );
preorder(tree.getRoot());
System.out.println();
System.out.print( "In-Order:" );
inorder(tree.getRoot());
System.out.println();
System.out.print( "Post-Order:" );
postorder(tree.getRoot());
System.out.println();
System.out.print( " Pre-Order:" );
iterativePreorder(tree.getRoot());
System.out.println();
System.out.print( "In-Order:" );
iterativeInorder(tree.getRoot());
System.out.println();
System.out.print( "Post-Order:" );
iterativePostorder(tree.getRoot());
System.out.println();
}
}

输出结果
Pre-Order:H D B A C G F E
In-Order:B A D C H G E F
Post-Order:A B C D E F G H
Pre-Order:H D B A C G F E
In-Order:B A D C H G E F
Post-Order:A B C D E F G H

本文出自 “子 孑” 博客，请务必保留此出处http://zhangjunhd.blog.51cto.com/113473/82616