【LeetCode每日一题】938. 二叉搜索树的范围和

输入：root = [10,5,15,3,7,null,18], low = 7, high = 15
输出：32

class Solution {
public:
    int rangeSumBST(TreeNode* root, int low, int high) {
        if (!root) return 0;
        int sum = 0;
        sum += rangeSumBST(root->left, low, high);
        if (root->val >= low && root->val <= high) sum += root->val;
        sum += rangeSumBST(root->right, low, high);
        return sum;
    }
};

class Solution {
public:
    int rangeSumBST(TreeNode* root, int low, int high) {
        if (!root) return 0;
        queue<TreeNode*> q;
        TreeNode* p = root;
        int sum = 0;
        while (p || q.size()) {
            while (p) {
                q.push(p);
                p = p->left;
            }
            if (q.size()) {
                p = q.front();
                q.pop();
                if (p->val >= low && p->val <= high) {
                    sum += p->val;
                }
                p = p->right;       
            }    
        }
        return sum;
    }
};