1、题目
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:
The number of nodes in the tree is at most 10000.
The final answer is guaranteed to be less than 2^31.
2、思路
对于一个根节点，可能落在区间内、区间左边和区间右边，所以可以递归计算，满足区间范围的节点和。
3、实现
public class Solution {
public int rangeSumBST(TreeNode root, int L, int R) {
if (root == null){
return 0;
}
int sum = 0;
if (root.val >= L && root.val <= R){
// 递归计算左子树+右子树和
sum = root.val + rangeSumBST(root.left, L, R) + rangeSumBST(root.right, L, R);
}else if (root.val < L){
// 左子树不可能存在满足区间的节点
sum = rangeSumBST(root.right, L, R);
}else if (root.val > R){
// 右子树上不可能存在满足区间的节点
sum = rangeSumBST(root.left, L, R);
}
return sum;
} }
