主要思路：中序遍历
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
int ans = 0;
public int rangeSumBST(TreeNode root, int low, int high) {
if(root==null) return 0;
rangeSumBST(root.left,low,high);
if(root.val>=low){
if(root.val<=high){
ans+=root.val;
}else{
return ans;
}
}
rangeSumBST(root.right,low,high);
return ans;
}
}