剑指offer 18：二叉树的镜像

二叉树的镜像

先序遍历

#include <iostream>
#include <stack>
#include <algorithm>
using namespace std;
struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;

    TreeNode(int x)
        : val(x), left(NULL), right(NULL)
    {

    }
};
class Solution
{
 public:
    void MirrorPre(TreeNode *root) {
        if (root == NULL) {
            return;
        }

        stack<TreeNode *> nstack;
        TreeNode *node = root;

        while (node != NULL || nstack.empty() != true) {
            while (node != NULL) {
                if (node->left != NULL && node->right != NULL) {
                    swap(node->left, node->right);
                }

                nstack.push(node);
                node = node->left;

            }//nstack.empty() == true

            if (nstack.empty() != true) {
                node = nstack.top();
                nstack.pop();
                node = node->right;
            }// node == NULL
        }

    } //没能理解

    
    //中序，后序
};