LeetCode日记 面试题27.二叉树的镜像

​​ https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof/​​

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode mirrorTree(TreeNode root) {
        if (root == null){
            return root;
        }

        TreeNode node = root.left;
        root.left = root.right;
        root.right = node;

        mirrorTree(root.left);
        mirrorTree(root.right);
        
        return root;
    }
}

2.非递归

class Solution {
    public TreeNode mirrorTree(TreeNode root) {
        if (root == null){
            return root;
        }
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        while(!stack.isEmpty()){
            TreeNode cur = stack.pop();
            if(cur.left!=null){
                stack.push(cur.left);
            }
            if(cur.right!=null){
                stack.push(cur.right);
            }
             TreeNode node = cur.left;
             cur.left = cur.right;
             cur.right = node;
        }
        return root;
    }
}