leetcode讲解--938. Range Sum of BST

938. Range Sum of BST

Given the root node of a binary search tree, return the sum of values of all nodes with value between L and R (inclusive).

The binary search tree is guaranteed to have unique values.

Example 1:

Input: root = [10,5,15,3,7,null,18], L = 7, R = 15
Output: 32

Example 2:

Input: root = [10,5,15,3,7,13,18,1,null,6], L = 6, R = 10
Output: 23

Note:

1. The number of nodes in the tree is at most 10000.
2. The final answer is guaranteed to be less than 2^31.

题目地址

这道题考察的是简单的二叉树遍历，你可以使用三种遍历中的任何一种（先序、中序、后序），下面我使用先序遍历来解题：

Java代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int result=0;
    public int rangeSumBST(TreeNode root, int L, int R) {
        if(root==null)
            return result;
        if(root.val>=L && root.val<=R){
                result += root.val;
            }
        rangeSumBST(root.left, L, R);
        rangeSumBST(root.right, L, R);
        return result;
    }
}