Diameter of binary tree + mirror exchange

#include<iostream>
#include<string>
using namespace std;
struct   TreeNode
{
    
    
	int val;
	struct   TreeNode*left;
	struct   TreeNode*right;
	TreeNode(int x):val(x),left(nullptr),right(nullptr){
    
    }
};
//二叉树的镜像
TreeNode* mirrorTree(TreeNode* root) {
    
    
	 if(root==nullptr)
	 {
    
    
		 return nullptr;
	 }
	 TreeNode*temp=root->left;
	 root->left=mirrorTree(root->right);
	 root->right=mirrorTree(temp);
	 return root;
    }

// 二叉树的最长路径和   直径
    int maxD = 0;
    int maxdepth(TreeNode* node){
    
    
        if(node == nullptr) return 0;
        int leftdepth = maxdepth(node->left);
        int rightdepth = maxdepth(node->right);
        maxD = max(maxD, leftdepth + rightdepth);
        return max(leftdepth, rightdepth) + 1;
    }
    int diameterOfBinaryTree(TreeNode* root) {
    
    
        maxdepth(root);
        return maxD;
    }
//树的创建
int N=0;
TreeNode* createTree(string&zfsz){
    
    
    if(zfsz[N]=='#'){
    
    
        N++;
        return NULL;
    }
    TreeNode* root= new TreeNode(zfsz[N]-48);
    N++;
    root->left=createTree(zfsz);
    root->right=createTree(zfsz);
    return root;
}
 //前序遍历
void pretree(TreeNode*root)
{
    
    
	if(root==nullptr)
		return ;
	cout<<root->val<<endl;
	pretree(root->left);
	pretree(root->right);
}
int main()
{
    
    
string str;
cin>>str;
TreeNode*root=createTree(str);
pretree(root);
//TreeNode*reroot=mirrorTree(root);
//pretree(reroot);
cout<<diameterOfBinaryTree(root)<<endl;
//  1246###5#7##3##
// 12##3##
	system("pause");
	return 0;
}