package com.springboot.study.tests.trees;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @Author: guodong
 * @Date: 2021/12/24 17:03
 * @Version: 1.0
 * @Description:
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class TreeNode {

    public int val;

    
 
public TreeNode left;

    public TreeNode right;

}

package com.springboot.study.tests.trees;

import java.util.*;

/**
 * @Author: guodong
 * @Date: 2021/12/24 17:05
 * @Version: 1.0
 * @Description:
 */
public class binaryTree {

    public static void main(String[] args) {
        List<Integer> list=new
 
 ArrayList<Integer>();
        //構造二叉樹
        TreeNode treeNode6=new TreeNode(2,null,null);
        TreeNode treeNode5=new TreeNode(1,null,null);
        TreeNode treeNode4=new TreeNode(7,null,null);
        TreeNode treeNode3=new TreeNode(6,treeNode5,treeNode6);
        TreeNode treeNode2=new TreeNode(5,treeNode4,null
 
);
        TreeNode root=new TreeNode(3,treeNode2,treeNode3);
        list=DFS(root);
        System.out.println("深度優先遍歷:"+list);
        list=BFS(root);
        System.out.println("廣度優先遍歷:"+list);
    }

    /**
     * 深度優先遍歷
     * @param root
     * @return
     */
    public static List<Integer> DFS(TreeNode root){
        Stack<TreeNode> stack=new Stack<TreeNode>();
        List<Integer> list=new ArrayList<Integer>();
        if(root==null)
            return list;
        stack.push(root);
        while (!stack.isEmpty()){
            TreeNode t=stack.pop();
            if(t.right!=null){ stack.push(t.right); }
            if(t.left!=null){ stack.push(t.left); }
            list.add(t.val);
        }
        return list;
    }

    /**
     * 廣度優先遍歷
     * @param root
     * @return
     */
    public static List<Integer> BFS(TreeNode root){
        Queue<TreeNode> queue=new LinkedList<TreeNode>();
        List<Integer> list=new ArrayList<Integer>();
        if(root==null){return list;}
        queue.add(root);
        while (!queue.isEmpty()){
            TreeNode t=queue.remove();
            if(t.left!=null){ queue.add(t.left); }
            if(t.right!=null){ queue.add(t.right); }
            list.add(t.val);
        }
        return list;
    }


}

1. 圖的深度優先遍歷是指，從⼀個節點出發，⼀直沿著邊向下深⼊去找節點，如果找不到了則返回上⼀層找其他節點
2. 圖的⼴度優先遍歷只是，從⼀個節點出發，向下先把第⼀層的節點遍歷完，再去遍歷第⼆層的節點，直到遍歷到最後⼀層