Find K Largest Elements in BST

来源：EPI

原帖：EPI 11.11. pg. 312.

题目：
Given the root of a BST and an integer k, design a function that finds the k largest elements in this BST. For example, if the input to your function is the BST in Figure 11.1 on Page 87 and k = 3, your function should return <53, 47, 43>.

代码：

 struct TreeNode {  
   int val;  
   TreeNode* left;  
   TreeNode* right;  
   TreeNode(int v) : val(v), left(NULL), right(NULL) {}  
 };  
   
   
 void find_k_largest_in_BST_helper(TreeNode* root, int k, vector<int> &k_elements) {  
   if (!root || k_element.size() == k) {  
     return;  
   }  
   // Perform reverse inorder traversal  
   if (root && k_elements.size() < k) {  
     find_k_largest_in_BST_helper(root->right, k, k_elements);  
     if (k_elements.size() < k) {  
       k_elements.push_back(root->val);  
       find_k_largest_in_BST_helper(root->left, k, k_elements);  
     }  
   }  
 }  
   
 vector<int> find_k_largest_in_BST(TreeNode* root, int k) {  
   vector<int> k_elements;  
   find_k_largest_in_BST_helper(root, k , k_elements);  
   return k_elements;  
 }