c++中序遍历，点到为止

class Solution {
public:
    TreeNode* KthNode(TreeNode* pRoot, int k)
    {
        if (!pRoot || k==0) return nullptr;
        array.clear();
        MidTrav(array, pRoot, k);
        if (array.size() < k) return nullptr;
        return array.back();
    }
private:
    vector<TreeNode*> array;
    void MidTrav(vector<TreeNode*>& array, TreeNode* root, int end)
    {
        if (!root || array.size() == end) return;
        MidTrav(array, root->left, end);
        if (array.size() == end) return;
        array.push_back(root);
        MidTrav(array, root->right, end);
    }
};