二叉搜索树第k个节点

 /*
 struct TreeNode {
     int val;
     struct TreeNode *left;
     struct TreeNode *right;
     TreeNode(int x) :
             val(x), left(NULL), right(NULL) {
     }
 };
 */
 class Solution {
 public:
     TreeNode* KthNode(TreeNode* pRoot, int k)
     {
         if(!pRoot) return nullptr;
         vector<TreeNode*> res;
         Sortnode(pRoot,res);
         if(k<= || k>res.size()) return nullptr;

         return res[k-];
     }
     void Sortnode(TreeNode* root,vector<TreeNode*>& vec){
         if(!root) return;
         Sortnode(root->left,vec);
         vec.push_back(root);
         Sortnode(root->right,vec);
     }
 };