二叉树非递归遍历方法

直接上代码

import java.util.LinkedList;class TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int x) {        val = x;    }}public class erchashubianli {    // 递归前序遍历    public static void preOrder1(TreeNode node) {        if (node == null)            return;        System.out.print(node.val + " ");        postOrder1(node.left);        postOrder1(node.right);    }    // 非递归前序遍历    public static void preOrder2(TreeNode node) {        LinkedList<TreeNode> list = new LinkedList<>();        TreeNode p = node;        while (p != null || !list.isEmpty()) {            while (p != null) {                System.out.print(p.val + " ");                list.add(p);                p = p.left;            }            if (!list.isEmpty()) {                p = list.removeLast();                p = p.right;            }        }    }    // 递归中序遍历    public static void midOrder1(TreeNode node) {        if (node == null)            return;        midOrder1(node.left);        System.out.print(node.val + " ");        midOrder1(node.right);    }    // 非递归中序遍历    public static void midOrder2(TreeNode node) {        LinkedList<TreeNode> list = new LinkedList<>();        TreeNode p = node;        while (p != null || !list.isEmpty()) {            while (p != null) {                list.add(p);                p = p.left;            }            if (!list.isEmpty()) {                p = list.removeLast();                System.out.print(p.val + " ");                p = p.right;            }        }    }    // 递归后序遍历    public static void postOrder1(TreeNode node) {        if (node == null)            return;        postOrder1(node.left);        postOrder1(node.right);        System.out.print(node.val + " ");    }    // 非递归后序遍历    public static void postOrder2(TreeNode node) {        class Temp {            boolean isFirst;            TreeNode node;            public Temp(TreeNode node, boolean isFirst) {                // TODO Auto-generated constructor stub                this.isFirst = isFirst;                this.node = node;            }        }        LinkedList<Temp> list = new LinkedList<>();        TreeNode p = node;        while (p != null || !list.isEmpty()) {            while (p != null) {                Temp tmp = new Temp(p, true);                list.add(tmp);                p = p.left;            }            if (!list.isEmpty()) {                Temp tmp = list.removeLast();                if (tmp.isFirst) {                    p = tmp.node.right;                    tmp.isFirst = false;                    list.add(tmp);                } else {                    p = null;                    System.out.print(tmp.node.val + " ");                }            }        }    }    public static void main(String[] args) {        TreeNode node1 = new TreeNode(1);        TreeNode node2 = new TreeNode(2);        TreeNode node3 = new TreeNode(3);        TreeNode node4 = new TreeNode(4);        TreeNode node5 = new TreeNode(5);        TreeNode node6 = new TreeNode(6);        node1.left = node2;        node1.right = node3;        node2.left = node4;        node2.right = node5;        node5.right = node6;        // 递归前序遍历        preOrder1(node1);        // 非递归前序遍历        System.out.println();        preOrder2(node1);        // 递归中序遍历        System.out.println();        midOrder1(node1);        // 非递归中序遍历        System.out.println();        midOrder2(node1);        // 递归后序遍历        System.out.println();        postOrder1(node1);        // 非递归后序遍历        System.out.println();        postOrder2(node1);    }}