二叉树的遍历学习

1.创建对象

package com.zl;

public class TreeNode {
    private String vlaue;
    private TreeNode leftTreeNode;
    private TreeNode rightTreeNode;


    public TreeNode(String vlaue, TreeNode leftTreeNode, TreeNode rightTreeNode) {
        this.vlaue = vlaue;
        this.leftTreeNode = leftTreeNode;
        this.rightTreeNode = rightTreeNode;
    }

    public String getVlaue() {
        return vlaue;
    }

    public void setVlaue(String vlaue) {
        this.vlaue = vlaue;
    }

    public TreeNode getLeftTreeNode() {
        return leftTreeNode;
    }

    public void setLeftTreeNode(TreeNode leftTreeNode) {
        this.leftTreeNode = leftTreeNode;
    }

    public TreeNode getRightTreeNode() {
        return rightTreeNode;
    }

    public void setRightTreeNode(TreeNode rightTreeNode) {
        this.rightTreeNode = rightTreeNode;
    }
}

 

2.遍历算法实现

package com.zl;

import java.util.LinkedList;
import java.util.Stack;

public class BinaryTree {

    /* 迭代方式 先序遍历二叉树 */
    public static void preOrderIteration(TreeNode tree) {
        Stack<TreeNode> stack = new Stack<>();
        while (true) {
            while (tree != null) {
                System.out.printf(tree.getVlaue() + "\t");
                stack.push(tree);
                tree = tree.getLeftTreeNode();
            }
            if (stack.empty()) {
                break;
            }
            TreeNode popTreeNode = stack.pop();
            tree = popTreeNode.getRightTreeNode();
        }
    }

    /* 迭代方式 中序遍历二叉树 */
    public static void midOrderIteration(TreeNode tree) {
        Stack<TreeNode> stack = new Stack<>();
        while (true) {
            while (tree != null) {
                stack.push(tree);
                tree = tree.getLeftTreeNode();
            }
            if (stack.empty()) {
                break;
            }
            TreeNode popTreeNode = stack.pop();
            System.out.printf(popTreeNode.getVlaue() + "\t");
            tree = popTreeNode.getRightTreeNode();
        }
    }

    /* 迭代方式 后序遍历二叉树 */
    public static void postOrderIteration(TreeNode tree) {
        TreeNode hasPrintTree = null;
        Stack<TreeNode> stack = new Stack<>();
        while (true) {
            while (tree != null) {
                stack.push(tree);
                tree = tree.getLeftTreeNode();
            }
            if (stack.empty()) {
                break;
            }
            if (stack.lastElement().getRightTreeNode() == null) {
                //1.右子树为空
                TreeNode treeNode = stack.pop();
                hasPrintTree = treeNode;
                System.out.print(treeNode.getVlaue() + "\t");
                tree = null;
            } else if (stack.lastElement().getRightTreeNode() == hasPrintTree) {
                //2.右子树不为空,且已经打印过了
                TreeNode treeNode = stack.pop();
                hasPrintTree = treeNode;
                System.out.print(treeNode.getVlaue() + "\t");
                tree = null;
            } else {
                //3.右子树不为空 没有打印过
                TreeNode rightTreeNode = stack.lastElement().getRightTreeNode();
                tree = rightTreeNode;
            }

        }
    }

    /* 迭代方式层序遍历二叉树 */
    public static void levelOrderIteration(TreeNode tree) {
        if (tree == null) return;
        LinkedList<TreeNode> treeNodeList = new LinkedList<>();
        treeNodeList.add(tree);

        while (!treeNodeList.isEmpty()) {
            TreeNode pushTree = treeNodeList.removeFirst();
            System.out.print(pushTree.getVlaue() + "\t");
            if (pushTree.getLeftTreeNode() != null) {
                treeNodeList.addLast(pushTree.getLeftTreeNode());
            }
            if (pushTree.getRightTreeNode() != null) {
                treeNodeList.addLast(pushTree.getRightTreeNode());
            }

        }


    }

    public static void main(String[] args) {
        //测试二叉树形式
        /*
             1
            / \
           2   3
          /   / \
         4   5   6
            / \
           7   8
                \
                 9
         */

        //构建二叉树
        TreeNode treeNode9 = new TreeNode("9", null, null);
        TreeNode treeNode4 = new TreeNode("4", null, null);
        TreeNode treeNode7 = new TreeNode("7", null, null);
        TreeNode treeNode6 = new TreeNode("6", null, null);
        TreeNode treeNode8 = new TreeNode("8", null, treeNode9);
        TreeNode treeNode2 = new TreeNode("2", treeNode4, null);
        TreeNode treeNode5 = new TreeNode("5", treeNode7, treeNode8);
        TreeNode treeNode3 = new TreeNode("3", treeNode5, treeNode6);
        TreeNode tree = new TreeNode("1", treeNode2, treeNode3);


        System.out.print("递归先序遍历tree:");
        preOrderRecursive(tree);
        System.out.print(System.lineSeparator());

        System.out.print("迭代先序遍历tree:");
        preOrderIteration(tree);
        System.out.print(System.lineSeparator());
        System.out.print(System.lineSeparator());

        System.out.print("递归中序遍历tree:");
        midOrderRecursive(tree);
        System.out.print(System.lineSeparator());

        System.out.print("迭代中序遍历tree:");
        midOrderIteration(tree);
        System.out.print(System.lineSeparator());
        System.out.print(System.lineSeparator());

        System.out.print("递归后序遍历tree:");
        postOrderRecursive(tree);
        System.out.print(System.lineSeparator());

        System.out.print("迭代后序遍历tree:");
        postOrderIteration(tree);
        System.out.print(System.lineSeparator());
        System.out.print(System.lineSeparator());

        System.out.print("迭代层序遍历tree:");
        levelOrderIteration(tree);
        System.out.print(System.lineSeparator());
        System.out.print(System.lineSeparator());


    }


    /* 递归方式先序遍历二叉树 */
    public static void preOrderRecursive(TreeNode tree) {
        if (null == tree) {
            return;
        } else {
            System.out.print(tree.getVlaue() + "\t");
            preOrderRecursive(tree.getLeftTreeNode());
            preOrderRecursive(tree.getRightTreeNode());
        }
    }


    /* 递归方式中序遍历二叉树 */
    public static void midOrderRecursive(TreeNode tree) {
        if (null == tree) {
            return;
        } else {
            midOrderRecursive(tree.getLeftTreeNode());
            System.out.print(tree.getVlaue() + "\t");
            midOrderRecursive(tree.getRightTreeNode());
        }
    }

    /* 递归方式后序遍历二叉树 */
    public static void postOrderRecursive(TreeNode tree) {
        if (null == tree) {
            return;
        } else {
            postOrderRecursive(tree.getLeftTreeNode());
            postOrderRecursive(tree.getRightTreeNode());
            System.out.print(tree.getVlaue() + "\t");
        }
    }

}