[数据结构与算法]二叉树前序中序后序遍历

一：前序中序后序

????????前序遍历: 先输出父节点，再遍历左子树和右子树

????????中序遍历: 先遍历左子树，再输出父节点，再遍历右子树

????????后序遍历: 先遍历左子树，再遍历右子树，最后输出父节点

????????小结: 看输出父节点的顺序，就确定是前序，中序还是后序

二：遍历思路

三：二叉树前序中序后序遍历

package com.atgguigu.tree;

public class BinaryTreeDemo {

    public static void main(String[] args) {
        HeroNode root = new HeroNode(1, "宋江");
        HeroNode node2 = new HeroNode(2, "吴用");
        HeroNode node3 = new HeroNode(3, "卢俊义");
        HeroNode node4 = new HeroNode(4, "林冲");
        HeroNode node5 = new HeroNode(5, "关胜");

        root.setLeft(node2);
        root.setRight(node3);
        node3.setRight(node4);
        node3.setLeft(node5);

        BinaryTree binaryTree = new BinaryTree(root);

        System.out.println("==========前序遍历==========");
        binaryTree.preOrder();
        System.out.println("==========中序遍历==========");
        binaryTree.infixOrder();
        System.out.println("==========后序遍历==========");
        binaryTree.postOrder();


    }

}


//二叉树
class BinaryTree{
    private HeroNode root;

    public BinaryTree(HeroNode root) {
        this.root = root;
    }

    //前序遍历
    public void preOrder(){
      if(this.root!=null){
          this.root.preOrder();
      }else {
          System.out.println("二叉树为空无法遍历");
      }
    }
    //中序遍历
    public void infixOrder(){
        if(this.root!=null){
            this.root.infixOrder();
        }else {
            System.out.println("二叉树为空无法遍历");
        }
    }
    //后序遍历
    public void postOrder(){
        if(this.root!=null){
            this.root.postOrder();
        }else {
            System.out.println("二叉树为空无法遍历");
        }
    }


}



//节点
class HeroNode{
    private int no;
    private String name;
    private HeroNode left;   //左节点
    private HeroNode right;  //右节点

    public HeroNode(int no, String name) {
        this.no = no;
        this.name = name;
    }

    public int getNo() {
        return no;
    }

    public void setNo(int no) {
        this.no = no;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public HeroNode getLeft() {
        return left;
    }

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

    public HeroNode getRight() {
        return right;
    }

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

    @Override
    public String toString() {
        return "HeroNode{" +
                "no=" + no +
                ", name='" + name + '\'' +
                '}';
    }

    //前序遍历
    public void preOrder(){
        System.out.println(this); //先输出父节点
        //左递归
        if(this.left!=null){
            this.left.preOrder();
        }
        //右递归
        if(this.right!=null){
            this.right.preOrder();
        }
    }
    //中序遍历
    public void infixOrder(){
        //左递归
        if(this.left!=null){
            this.left.infixOrder();
        }
        System.out.println(this); //先输出父节点
        //右递归
        if(this.right!=null){
            this.right.infixOrder();
        }
    }
    //后序遍历
    public void postOrder(){
        //左递归
        if(this.left!=null){
            this.left.postOrder();
        }
        //右递归
        if(this.right!=null){
            this.right.postOrder();
        }
        System.out.println(this); //先输出父节点
    }

}

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