Java实现二叉树的遍历（多种方式实现前中后序的遍历）

二叉树的Node节点：

public class Node {private char key ;private Node left ;private Node right ;public Node() {}public Node(char key){this(key,null,null);}public Node(char key,Node left,Node right){this.key = key ;this.left = left ;this.right = right;}public char getKey() {return key;}public void setKey(char key) {this.key = key;}public Node getLeft() {return left;}public void setLeft(Node left) {this.left = left;}public Node getRight() {return right;}public void setRight(Node right) {this.right = right;}}

二叉树的遍历操作：

import java.util.Stack;public class BinaryTree {private Node root ;public BinaryTree(Node root) {this.root = root;}public Node getRoot(){return root ;}/*构造树*/public static Node init(){Node a = new Node('A');            Node b = new Node('B', null, a);            Node c = new Node('C');            Node d = new Node('D', b, c);            Node e = new Node('E');            Node f = new Node('F', e, null);            Node g = new Node('G', null, f);            Node h = new Node('H', d, g);            return h; // root} /*访问节点*/public static void visit(Node p){System.out.print(p.getKey()+" ");} /****************递归遍历二叉树**************************//*前序递归遍历*/public static void preOrder(Node root){if(root!=null){visit(root);preOrder(root.getLeft());preOrder(root.getRight());}}/*中序递归遍历*/public static void InOrder(Node root){if(root!=null){InOrder(root.getLeft());visit(root);InOrder(root.getRight());}}/*后序递归遍历*/public static void PostOrder(Node root){if(root!=null){PostOrder(root.getLeft());PostOrder(root.getRight());visit(root);}}/*************非递归遍历*******************//*前序非递归遍历*/public static void iterativePreorder(Node p){Stack<Node> stack = new Stack<Node>();if(p!=null){stack.push(p);while(!stack.isEmpty()){p = stack.pop();visit(p);if(p.getRight()!=null){stack.push(p.getRight());}if(p.getLeft()!=null){stack.push(p.getLeft());}}}}public static void iterativePreorder2(Node p){Stack<Node> stack = new Stack<Node>();while(p!=null || !stack.empty()){if(p!=null){//while(p!=null)visit(p);stack.push(p);p=p.getLeft();}else{p=stack.pop();p=p.getRight();}}}public static void iterativePreorder3(Node p){Stack<Node> stack = new Stack<Node>();while(p!=null || stack.size()>0){while(p!=null){//if(p!=null)visit(p);stack.push(p);p=p.getLeft();}if(stack.size()>0){p=stack.pop();p=p.getRight();}}}/*中序非递归遍历*/public static void iterativeInorder(Node p){Stack<Node> stack = new Stack<Node>();while(p!=null){while(p!=null){if(p.getRight()!=null)stack.push(p.getRight());stack.push(p);p=p.getLeft();}p=stack.pop();while(!stack.isEmpty() && p.getRight()==null){visit(p);p=stack.pop();}visit(p);if(!stack.isEmpty())p=stack.pop();elsep=null;}}public static void iterativeInorder2(Node p){Stack<Node> stack = new Stack<Node>();while(p!=null||!stack.isEmpty()){if(p!=null){//while(p!=null)stack.push(p);p=p.getLeft();}else{p=stack.pop();visit(p);p=p.getRight();}}}/*后序非递归遍历*/public static void iterativePostorder(Node p){Node q = p ;//记录被访问过的节点Stack<Node> stack = new Stack<Node>();while(p!=null){//左子树入栈 for(;p.getLeft()!=null;p=p.getLeft()){stack.push(p);}//当左子树全部入栈结束，判断当前节点是否有右子树或者右子树没有被访问时输出当前节点while(p!=null &&(p.getRight()==null || p.getRight()==q)){visit(p);q=p;//记录被访问的节点if(stack.isEmpty())return ;p=stack.pop();}//右子树入栈stack.push(p);p=p.getRight();}}//双栈实现树的后序非递归遍历public static void iterativePostorder2(Node p){Stack<Node> stack1 = new Stack<Node>();Stack<Node> stack2 = new Stack<Node>();stack1.push(p);while(!stack1.isEmpty()){p = stack1.pop();stack2.push(p);if(p.getLeft()!=null)stack1.push(p.getLeft());if(p.getRight()!=null)stack1.push(p.getRight());}while(!stack2.isEmpty()){System.out.print(stack2.pop().getKey()+" ");}}public static void main(String[] args) {Node root = init();System.out.println("*****前序递归遍历*******");preOrder(root);System.out.println();iterativePreorder(root);System.out.println();iterativePreorder2(root);iterativePreorder3(root);System.out.println();System.out.println("*****中序递归遍历******");InOrder(root);System.out.println();iterativeInorder(root);System.out.println();iterativeInorder2(root);System.out.println();System.out.println("*****后序递归遍历*******");PostOrder(root);System.out.println();iterativePostorder(root);System.out.println();iterativePostorder2(root);}}