leetcode 938. Range Sum of BST

Seawolf

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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int rangeSumBST(TreeNode root, int L, int R) {
        if(root == null) return 0;
        return sum(root,L,R);
    }
    
    public int sum(TreeNode root, int L, int R){
        
        if(root == null) return 0;
        if(root.val >= L && root.val <= R) return root.val + sum(root.left,L,R) + sum(root.right,L,R);
        else if(root.val < L) return sum(root.right ,L,R);
        else return sum(root.left, L,R);
    }
}