> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/trees/sum-of-k-smallest-elements-in-bst.md).

# Sum of k smallest elements in BST

Given[ Binary Search Tree](http://quiz.geeksforgeeks.org/binary-search-tree-set-1-search-and-insertion/). The task is to find sum of all elements smaller than and equal to Kth smallest element.

**Examples:**

```
Input :  K = 3
              8
            /   \
           7     10
         /      /   \
        2      9     13
Output : 17
Explanation : Kth smallest element is 8 so sum of all
              element smaller then or equal to 8 are
              2 + 7 + 8

Input : K = 5
           8
         /   \
        5    11
      /  \
     2    7
      \
       3
Output :  25
```

```java
class Solution {
    int count = 0;
    int sum = 0;

    public int kthSmallest(TreeNode root, int k) {
        traverse(root, k);
        return sum;
    }

    public void traverse(TreeNode root, int k) {
        if (root == null)
            return;
        traverse(root.left, k);
        count++;
        if (count <= k)
            sum += root.val;
        if (count < k)
            traverse(root.right, k);
    }
}
```