数据结构 - 树(二叉树的前序、中序、后序遍历)

缺乏、安全感 2023-07-03 03:30 173阅读 0赞

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# 二叉树遍历（前序中序后序，主要是看父节点的输出顺序） #

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package tree;
    
    public class BinaryTreeDemo { 
        public static void main(String[] args) { 
            //先需要创建一颗二叉树
            BinaryTree binaryTree = new BinaryTree();
    
            //创建需要的节点
            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");
    
            //说明，先手动创建该二叉树，后面学习递归方式创建二叉树
            binaryTree.setRoot(root);
            root.setLeft(node2);
            root.setRight(node3);
            node3.setRight(node4);
    
            //测试
            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();
        }
    }
    
    class BinaryTree{ 
        private HeroNode root;
        public void setRoot(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");
            }
        }
    }
    class HeroNode{ 
        private int no;
        private String name;
        private HeroNode left;//默认null
        private HeroNode right;//默认null;
    
        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 + '\'' +
                    '}';
        }
        //编写前序遍历方法
        public void preOrder(){ 
            System.out.println(this);//先输出父节点
            //递归向左子树前序遍历
            if (this.left != null){ 
                this.left.preOrder();
            }
            //递归向右子树前序遍历
            if (this.right != null){ 
                this.right.preOrder();
            }
        }
        //编写中序遍历方法
        public void infixOrder(){ 
    
            //递归向左子树前序遍历
            if (this.left != null){ 
                this.left.infixOrder();
            }
    
            System.out.println(this);//输出父节点
    
            //递归向右子树前序遍历
            if (this.right != null){ 
                this.right.infixOrder();
            }
        }
        //编写后序遍历方法
        public void postOrder(){ 
            if (this.left != null){ 
                this.left.postOrder();
            }
    
            if (this.right != null){ 
                this.right.postOrder();
            }
            System.out.println(this);
        }
    }

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### 先纸上自己写了一遍，然后程序验证 ###

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