938. Range Sum of BST*
https://leetcode.com/problems/range-sum-of-bst/
题目描述
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
.
C++ 实现 1
实际上本题就是一个二分搜索树的遍历过程. 下面代码中使用前序遍历. 用递归方法方便理解, 减小了解题难度.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
private:
void preOrder(TreeNode *root, int L, int R, int &sum) {
if (!root) return;
if (root->val >= L && root->val <= R) sum += root->val;
preOrder(root->left, L, R, sum);
preOrder(root->right, L, R, sum);
}
public:
int rangeSumBST(TreeNode* root, int L, int R) {
int sum = 0;
preOrder(root, L, R, sum);
return sum;
}
};