算法之二叉树遍历

【代码示例】

package com.wcs.java;
import java.util.ArrayList;
import java.util.List;

public class BinaryTree { 

    class TreeNode {

        public String data; //数据

        public TreeNode leftNode; //左子树

        public TreeNode rightNode; //右子树

        public TreeNode(String data, TreeNode leftNode, TreeNode rightNode) {
            this.data = data;
            this.leftNode = leftNode;
            this.rightNode = rightNode;
        }

        /**
         * @return the data
         */
        public String getData() {
            return data;
        }

        /**
         * @param data the data to set
         */
        public void setData(String data) {
            this.data = data;
        }

        /**
         * @return the leftNode
         */
        public TreeNode getLeftNode() {
            return leftNode;
        }

        /**
         * @param leftNode the leftNode to set
         */
        public void setLeftNode(TreeNode leftNode) {
            this.leftNode = leftNode;
        }

        /**
         * @return the rightNode
         */
        public TreeNode getRightNode() {
            return rightNode;
        }

        /**
         * @param rightNode the rightNode to set
         */
        public void setRightNode(TreeNode rightNode) {
            this.rightNode = rightNode;
        }
    }

    public TreeNode init() {
        TreeNode B = new TreeNode("B", null, null);
        TreeNode D = new TreeNode("D", null, B);
        TreeNode C = new TreeNode("C", D, null);

        TreeNode J = new TreeNode("J", null, null);
        TreeNode I = new TreeNode("I", J, null);
        TreeNode G = new TreeNode("G", I, null);
        TreeNode F = new TreeNode("F", null, G);
        TreeNode H = new TreeNode("H", null, null);
        TreeNode E = new TreeNode("E", F, H);

        TreeNode A = new TreeNode("A", C, E);

        return A;
    }

    private static List<String> list;

    public String printOut() {
        StringBuffer stringBuffer = new StringBuffer();
        for(int i=0; i<list.size(); i++) {
            stringBuffer.append(list.get(i) + (i!=list.size()-1 ? "-" : ""));
        }
        return stringBuffer.toString();
    }

    public void  preorderTraversal(TreeNode node) { //递归先序遍历
        if(node != null && node.getData() != null) {
            list.add(node.getData());
            if(node.getLeftNode() != null && node.getLeftNode().getData() != null) { //左子树不为空
                preorderTraversal(node.getLeftNode());
            }
            if(node.getRightNode() != null && node.getRightNode().getData() != null) { //右子树不为空
                preorderTraversal(node.getRightNode());
            }
        }
    }

    public void inorderTraversal(TreeNode node) { //递归中序遍历
        if(node != null && node.getData() != null) {
            if(node.getLeftNode() != null && node.getLeftNode().getData() != null) {
                inorderTraversal(node.getLeftNode());
            }
            list.add(node.getData());
            if(node.getRightNode() != null && node.getRightNode().getData() != null) {
                inorderTraversal(node.getRightNode());
            }
        }
    }

    public void postorderTraversal(TreeNode node) { //递归后序遍历
        if(node != null && node.getData() != null) {
            if(node.getLeftNode() != null && node.getLeftNode().getData() != null) {
                postorderTraversal(node.getLeftNode());
            }
            if(node.getRightNode() != null && node.getRightNode().getData() != null) {
                postorderTraversal(node.getRightNode());
            }
            list.add(node.getData());
        }
    }

    public static void main(String[] args) {
        //二叉树初始化
        BinaryTree binaryTree = new BinaryTree();
        TreeNode treeNode = binaryTree.init();
        //先序遍历
        list = new ArrayList<String>();
        binaryTree.preorderTraversal(treeNode);
        System.out.println("先序遍历: " + binaryTree.printOut());
        //中序遍历
        list = new ArrayList<String>();
        binaryTree.inorderTraversal(treeNode);
        System.out.println("中序遍历: " + binaryTree.printOut());
        //后序遍历
        list = new ArrayList<String>();
        binaryTree.postorderTraversal(treeNode);
        System.out.println("后序遍历: " + binaryTree.printOut());
    }

}

【二叉树】

【运行结果】

先序遍历: A-C-D-B-E-F-G-I-J-H

中序遍历: D-B-C-A-F-J-I-G-E-H

后序遍历: B-D-C-J-I-G-F-H-E-A

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