二叉樹遍歷（前序中序后序，主要是看父節點的輸出順序）

package tree;public class BinaryTreeDemo {public static void main(String[] args) {//先需要創建一顆二叉樹BinaryTree binaryTree = new BinaryTree();//創建需要的節點HeroNode root = new HeroNode(1, "宋江");HeroNode node2 = new HeroNode(2, "吳用");HeroNode node3 = new HeroNode(3, "盧俊義");HeroNode node4 = new HeroNode(4, "林沖");//說明，先手動創建該二叉樹，后面學習遞歸方式創建二叉樹binaryTree.setRoot(root);root.setLeft(node2);root.setRight(node3);node3.setRight(node4);//測試System.out.println("前序遍歷");binaryTree.preOrder();System.out.println("中序遍歷");binaryTree.infixOrder();System.out.println("后序遍歷");binaryTree.postOrder();} }class BinaryTree{private HeroNode root;public void setRoot(HeroNode root){this.root = root;}//前序遍歷public void preOrder(){if (this.root != null){this.root.preOrder();}else {System.out.println("二叉樹為空無法遍歷");}}//中序遍歷public void infixOrder(){if (this.root != null){this.root.infixOrder();}else {System.out.println("二叉樹為空無法遍歷");}}//后序遍歷public void postOrder(){if (this.root != null){this.root.postOrder();}else {System.out.println("二叉樹為空無法遍歷");}} } class HeroNode{private int no;private String name;private HeroNode left;//默認nullprivate HeroNode right;//默認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;}@Overridepublic String toString() {return "HeroNode{" +"no=" + no +", name='" + name + '\'' +'}';}//編寫前序遍歷方法public void preOrder(){System.out.println(this);//先輸出父節點//遞歸向左子樹前序遍歷if (this.left != null){this.left.preOrder();}//遞歸向右子樹前序遍歷if (this.right != null){this.right.preOrder();}}//編寫中序遍歷方法public void infixOrder(){//遞歸向左子樹前序遍歷if (this.left != null){this.left.infixOrder();}System.out.println(this);//輸出父節點//遞歸向右子樹前序遍歷if (this.right != null){this.right.infixOrder();}}//編寫后序遍歷方法public void postOrder(){if (this.left != null){this.left.postOrder();}if (this.right != null){this.right.postOrder();}System.out.println(this);} }

先紙上自己寫了一遍，然后程序驗證

總結

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