938. Range Sum of BST

Traversal Approaches

• We can solve this problem with any of the traversal for the tree.
• We just need to check for the condition of the node value and then add the value to the sum.

BST Traversal

• We can use BST properties and avoid extra recursive calls.
• TC: O(N), N is number of nodes in the tree.
• SC: O(h), h is the height of the tree.

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