題目：給定一顆二叉搜尋樹，請找出其中的第k大的結點。例如， 5 / \ 3 7 /\ /\ 2 4 6 8 中，按結點數值大小順序第三個結點的值為4。

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, unsigned int k)
    {
        if(pRoot == NULL)
            return NULL;
        TreeNode* ObjNode = NULL;  
        KthNode(pRoot, &ObjNode, k);
        return ObjNode;
    }
    void KthNode(TreeNode* pRoot, TreeNode** ObjNode, unsigned int &k)
    {
        if(pRoot->left != NULL)
            KthNode(pRoot->left, ObjNode, k);
        if(*ObjNode == NULL)
        {
            if(k == 1)
            {
                *ObjNode = pRoot;
            }
            k--;
        }
        
        if(*ObjNode == NULL && pRoot->right != NULL)
            KthNode(pRoot->right, ObjNode, k);
    }
};