二叉树前序、中序、后序、层序遍历的递归与非递归java实现_对九个数用java按照前序遍历的法则进行输出-优快云博客

本文链接：https://blog.youkuaiyun.com/zjbzlc/article/details/101467268

本文详细介绍了二叉树的遍历算法，包括先序、中序、后序及层序遍历的递归与非递归实现。通过具体的Java代码示例，深入解析了各种遍历方式的工作原理，并提供了一个测试用例来验证算法的正确性。

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import java.util.Queue;
import java.util.Stack;
import java.util.concurrent.LinkedBlockingQueue;

public class TreeTraverse {

    public static void main(String[] args){
        //测试如下二叉树
//                   1
//                /     \
//              2         3
//            /    \    /    \
//           4      5  6      7

        Node root = new Node(1);
        root.left = new Node(2);
        root.left.left = new Node(4);
        root.left.right = new Node(5);
        root.right = new Node(3);
        root.right.left = new Node(6);
        root.right.right = new Node(7);
        preOrderTraverse(root);
        System.out.println();
        preOrderTraverse2(root);
        System.out.println();
        inOrderTraverse(root);
        System.out.println();
        inOrderTraverse2(root);
        System.out.println();
        posOrderTraverse(root);
        System.out.println();
        posOrderTraverse2(root);
        System.out.println();
        floorTraverse(root);
    }

    //先序遍历的递归实现
    public static void preOrderTraverse(Node node){
        if(node == null)
            return;
        System.out.print(node.value + "  ");
        preOrderTraverse(node.left);
        preOrderTraverse(node.right);
    }

    //先序遍历的非递归实现
    public static void preOrderTraverse2(Node node){
        if(node == null)
            return;
        Stack<Node> stack = new Stack<>();
        stack.push(node);
        while(!stack.isEmpty()){
            node = stack.pop();
            System.out.print(node.value + "  ");
            if(node.right != null)
                stack.push(node.right);
            if(node.left != null)
                stack.push(node.left);
        }
    }

    //中序遍历的递归实现
    public static void inOrderTraverse(Node node){
        if(node == null)
            return;
        inOrderTraverse(node.left);
        System.out.print(node.value + "  ");
        inOrderTraverse(node.right);
    }

    //中序遍历的非递归实现
    public static void inOrderTraverse2(Node node){
        if(node == null)
            return;
       Stack<Node> stack = new Stack<>();
       while(!stack.isEmpty() || node != null){
           while(node != null){
               stack.push(node);
               node = node.left;
           }
           node = stack.pop();
           System.out.print(node.value + "  ");
           node = node.right;
       }
    }

    //后序遍历的递归实现
    public static void posOrderTraverse(Node node){
        if(node == null)
            return;
        posOrderTraverse(node.left);
        posOrderTraverse(node.right);
        System.out.print(node.value + "  ");
    }

    //后序遍历的非递归实现
    public static void posOrderTraverse2(Node node){
        if(node == null)
            return;
        Stack<Node> stack = new Stack<>();
        Stack<Node> help = new Stack<>();
        stack.push(node);
        while(!stack.isEmpty()){
            node = stack.pop();
            help.push(node);
            if(node.left != null)
                stack.push(node.left);
            if(node.right != null)
                stack.push(node.right);
        }
        while(!help.isEmpty())
            System.out.print(help.pop().value + "  ");
    }

    //层序遍历
    public static void floorTraverse(Node node){
        if(node == null)
            return;
        Queue<Node> queue = new LinkedBlockingQueue<>();
        queue.add(node);
        while(!queue.isEmpty()){
            node = queue.poll();
            System.out.print(node.value + "  ");
            if(node.left != null)
                queue.add(node.left);
            if(node.right != null)
                queue.add(node.right);
        }
    }
}

class Node{
    int value;
    Node left;
    Node right;
    public Node(int value){
        this.value = value;
        this.left = null;
        this.right = null;
    }
}