剑指offer:面试题19、二叉树的镜像

题目描述

操作给定的二叉树，将其变换为源二叉树的镜像。

二叉树的镜像定义：
源二叉树
8
/ \
6 10
/ \ / \
5 7 9 11
镜像二叉树
8
/ \
10 6
/ \ / \
11 9 7 5

代码示例

public class Offer19 {
    public static void main(String[] args) {
        //构建树
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        //测试二叉树的镜像，使用先序遍历打印验证
        Offer19 testObj = new Offer19();
        testObj.preOrder(root);
        System.out.println();
        testObj.mirror(root);
        testObj.preOrder(root);
    }

    static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }
    //将二叉树进行镜像
    public void mirror(TreeNode root) {
        if (root == null)
            return;
        swap(root);
        mirror(root.left);
        mirror(root.right);
    }
    //交换当前节点的左右子树
    private void swap(TreeNode root) {
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
    }
    //二叉树先序遍历
    private void preOrder(TreeNode root) {
        if (root == null)
            return;
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }
}