二叉树建树的过程

#include <iostream>
using namespace std;
//二叉树建树的过程 
struct tree{
    char data;
    tree* left;
    tree* right;
};
tree *creat(tree *root){
    char ch;
    scanf("%c", &ch);
    if(ch == ','){
        root = NULL;
    }else{
        root = new tree;
        root->data = ch;
        root->left = creat(root->left);
        root->right = creat(root->right );
    }
    return root;
}
tree *build(int ps, int is, int n){
    //preorder为先序遍历序列，inorder为中序遍历序列
    //ps为先序的起始位置，is为中序的起始位置，n为序列元素个数
    int k;
    for(k = is; k <= is + n-1; k++){
        if(preorder[ps] == inorder[k])
        break;
    } 
    tree *t = new tree;
    t->data = preorder[ps];
    //当中序遍历序列的起始位置为根节点时说明该树无左子树 
    if(k == is) t->left = NULL;
    else t->left = build(ps + 1, is, k - is);//递归建立左子树    
    //当中序遍历序列的最后一个元素是根节点时说明
    //该节点无右子树 
    if(k == is + n - 1){
        t->right = NULL; 
    }else{
        t->right = build(ps + 1 + (k - is), k + 1, n - (k - is) - 1);
    }
    return t;
}
int main(){
    return 0;
}