#include <bits/stdc++.h>
using namespace std;

struct tnode{
    char val;
    tnode *left,*right;
    tnode():val(' '),left(nullptr),right(nullptr){}
    tnode(char c):val(c),left(nullptr),right(nullptr){}
};

//寻找式插入
tnode* insert(tnode*root,char val){
    if(root==nullptr)return new tnode(val);
    if(val<root->val)root->left=insert(root->left,val);
    else if(val>root->val)root->right=insert(root->right,val);
    return root;
}

tnode *buildTree(string s){
    tnode *root=nullptr;
    for(auto x:s){
        root=insert(root,x);
    }
    return root;
}

void preOrder(tnode*root,string &ans){
    if(root==nullptr)return;
    ans.push_back(root->val);
    preOrder(root->left,ans);
    preOrder(root->right,ans);
}

void inOrder(tnode*root,string &ans){
    if(root==nullptr)return;
    inOrder(root->left,ans);
    ans.push_back(root->val);
    inOrder(root->right,ans);
}

int main(){
...