/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int rangeSumBST(TreeNode* root, int low, int high) {
        queue<TreeNode*> q;
        if(root != nullptr){
            q.push(root);
        }else{
            return 0;
        }
        TreeNode* cur;
        int sum = 0;
        while(!q.empty()){
            cur = q.front();
            q.pop();
            int tmp = cur->val;
            if(tmp >= low && tmp <= high){
                sum += tmp;
            }
            if(cur->left != nullptr){
                q.push(cur->left);
            }
            if(cur->right != nullptr){
                q.push(cur->right);
            }
        }
        return sum;
    }
};