二叉树遍历二叉树遍历先序中序后序层次二叉树结点手动生成图中二叉树先序遍历根节点->左结点->右结点输出结果->FBADC

二叉树遍历

先序
中序
后序
层次

二叉树结点

import lombok.Data;
@Data
public class TreeNode {
    private String value;
    private TreeNode left;
    private TreeNode right;
    public TreeNode(String value) {
        this.value = value;
    }
}

手动生成图中二叉树

        TreeNode treeNode1 = new TreeNode("F");
        TreeNode treeNode2 = new TreeNode("B");
        TreeNode treeNode3 = new TreeNode("G");
        TreeNode treeNode4 = new TreeNode("A");
        TreeNode treeNode5 = new TreeNode("D");
        TreeNode treeNode6 = new TreeNode("I");
        TreeNode treeNode7 = new TreeNode("C");
        TreeNode treeNode8 = new TreeNode("E");
        TreeNode treeNode9 = new TreeNode("H");
        treeNode1.setLeft(treeNode2);
        treeNode1.setRight(treeNode3);
        treeNode2.setLeft(treeNode4);
        treeNode2.setRight(treeNode5);
        treeNode5.setLeft(treeNode7);
        treeNode5.setRight(treeNode8);
        treeNode3.setRight(treeNode6);
        treeNode6.setLeft(treeNode9);

先序遍历

根节点 -> 左结点 -> 右结点
输出结果 -> F B A D C E G I H

    public static void preOrder(TreeNode treeNode) {
        if (treeNode == null) {
            return;
        }
        System.out.print(treeNode.getValue() + " ");
        preOrder(treeNode.getLeft());
        preOrder(treeNode.getRight());
    }

中序遍历

左结点 -> 根节点 -> 右结点
输出结果 -> A B C D E F G H I

    public static void midOrder(TreeNode treeNode) {
        if (treeNode == null) {
            return;
        }
        midOrder(treeNode.getLeft());
        System.out.print(treeNode.getValue() + " ");
        midOrder(treeNode.getRight());
    }

后序遍历

右结点 -> 左结点 -> 根节点
输出结果 -> A B C D E G H I F

    public static void midOrder(TreeNode treeNode) {
        if (treeNode == null) {
            return;
        }
        midOrder(treeNode.getLeft());
        System.out.print(treeNode.getValue() + " ");
        midOrder(treeNode.getRight());
    }

层序遍历

输出结果 -> F B G A D I C E H

    public static void levelOrder(TreeNode treeNode) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(treeNode);
        while (!queue.isEmpty()) {
            TreeNode temp = queue.poll();
            System.out.print(temp.getValue() + " ");
            if (temp.getLeft() != null) {
                queue.add(temp.getLeft());
            }
            if (temp.getRight() != null) {
                queue.add(temp.getRight());
            }
        }
    }