已知先序序列和中序序列求二叉树用c++实现

以下是用C++实现已知先序序列和中序序列求二叉树的代码：

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
};

class Solution {
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        unordered_map<int, int> inorder_map;
        for (int i = 0; i < inorder.size(); i++) {
            inorder_map[inorder[i]] = i;
        }
        return buildTreeHelper(preorder, 0, preorder.size() - 1, inorder, 0, inorder.size() - 1, inorder_map);
    }

    TreeNode* buildTreeHelper(vector<int>& preorder, int pre_start, int pre_end, vector<int>& inorder, int in_start, int in_end, unordered_map<int, int>& inorder_map) {
        if (pre_start > pre_end || in_start > in_end) {
            return nullptr;
        }
        int root_val = preorder[pre_start];
        TreeNode* root = new TreeNode(root_val);
        int inorder_root_index = inorder_map[root_val];
        int left_subtree_size = inorder_root_index - in_start;
        root->left = buildTreeHelper(preorder, pre_start + 1, pre_start + left_subtree_size, inorder, in_start, inorder_root_index - 1, inorder_map);
        root->right = buildTreeHelper(preorder, pre_start + left_subtree_size + 1, pre_end, inorder, inorder_root_index + 1, in_end, inorder_map);
        return root;
    }
};

int main() {
    vector<int> preorder = {3, 9, 20, 15, 7};
    vector<int> inorder = {9, 3, 15, 20, 7};
    Solution solution;
    TreeNode* root = solution.buildTree(preorder, inorder);
    return 0;
}