我不会做抽卡会歪吗?

#include <bits/stdc++.h>
using namespace std;
struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
int sum(TreeNode* root) {
    if (root==NULL) return 0;
    if (root->left==NULL&&root->right==NULL) return root->val;
    return sum(root->left) + sum(root->right);
}TreeNode* build(vector<int>& t,int index) {
    if (index>=t.size()) return NULL;
    TreeNode* node = new TreeNode(t[index]);
    node->left=build(t,2 * index + 1);
    node->right=build(t,2 * index + 2);
    return node;
}
int main() {
    int n;
    while (cin >> n && n!= 0) {
    	vector<int> t(n);
        for (int i = 0; i < n; ++i) cin>>t[i];
        TreeNode* root=build(t,0);
        cout<<sum(root)<<endl;
    }
}

TJ：听凭风引 且听风吟 solution - 洛谷专栏 (luogu.com.cn)