Description Title

given a binary search tree, find the k-th smaller nodes therein. For example, (5,3,7,2,4,6,8), the numerical values according to the third junction point is 4 summary.

Solution: In order traversal, consider k <= 0 and where k is greater than the total number of nodes

```
class Solution {
int cnt = 0;
TreeNode * knode = NULL;
public:
void DFS(TreeNode* pRoot, int k)
{
if (pRoot->left && cnt<k)
DFS(pRoot->left, k);
if (++cnt == k)
knode = pRoot;
if (pRoot->right && cnt<k)
DFS(pRoot->right, k);
}
TreeNode* KthNode(TreeNode* pRoot, int k)
{
if (pRoot==NULL || k <= 0)
return NULL;
DFS(pRoot, k);
return knode;
}
};
```