Range Sum of BST

LeetCode Q 938 - Range Sum of BST

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).
The binary search tree is guaranteed to have unique values.

Example 1: Input: root = [10,5,15,3,7,null,18], L = 7, R = 15 ; Output: 32
Example 2: Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10 ; Output: 23

Note:

• The number of nodes in the tree is at most 10000.
• The final answer is guaranteed to be less than 2^31.

Solution: DFS

Code:

private int sum = 0;
public int rangeSumBST(TreeNode root, int L, int R) {
  dfs(root, L, R);
  return sum;
}

private void dfs(TreeNode root, int L, int R) {
  if (root == null) return;
  
  if (root.val >= L && root.val <= R) 
      sum += root.val;
  
  if (L < root.val)
    dfs(root.left, L, R);
  
  if (root.val < R)
    dfs(root.right, L, R);   
}