题解 | #二叉树的镜像#

整了半天发现只需要最小颗粒度到 RTL 交换 RL 分别压入 Stack 就行了，本来以为是个星耀王者，结果是个一星白银

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return TreeNode类
     */
    public TreeNode Mirror (TreeNode pRoot) {
        // write code here
        if(pRoot == null){
            return pRoot;
        }
        Deque<TreeNode> stack = new LinkedList<>();
        stack.push(pRoot);
        while(!stack.isEmpty()){
            TreeNode node = stack.pop();
            if(node != null){
                TreeNode left = node.left;
                node.left = node.right;
                stack.push(node.left);
                node.right = left;
                stack.push(node.right);
            }
        }
        return pRoot;
    }
}