[leetcode #938] Range Sum of BST

Problem

Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high].

Example 1:

Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
Output: 32
Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
Output: 23
Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.

Constraints:

・ The number of nodes in the tree is in the range [1, 2 * 10⁴].
・ 1 <= Node.val <= 10⁵
・ 1 <= low <= high <= 10⁵
・ All Node.val are unique.

Idea

트리를 탐색하면서 범위에 해당하는 값이라면 sum 값에 더하면 된다.

트리 탐색이 끝나고 sum을 리턴하면 끝!

Solution

/**
 * 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 sum = 0;

    public int rangeSumBST(TreeNode root, int low, int high) {
        traverse(root, low, high);

        return sum;
    }

    private void traverse(TreeNode node, int low, int high) {
        if (node == null) {
            return;
        }

        if (node.val >= low && node.val <= high) {
            sum += node.val;        
        }

        traverse(node.left, low, high);
        traverse(node.right, low, high);
    }
}

Reference

https://leetcode.com/problems/range-sum-of-bst/submissions/