# 938. Range Sum of BST 二叉搜索树的范围和

@TOC

## # 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:

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

## # 解题方法

### # 递归

``````# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def rangeSumBST(self, root, L, R):
"""
:type root: TreeNode
:type L: int
:type R: int
:rtype: int
"""
if not root:
return 0
res = 0
if L <= root.val <= R:
res += root.val
res += self.rangeSumBST(root.left, L, R)
res += self.rangeSumBST(root.right, L, R)
elif root.val < L:
res += self.rangeSumBST(root.right, L, R)
elif root.val > R:
res += self.rangeSumBST(root.left, L, R)
return res
``````

``````# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def rangeSumBST(self, root, L, R):
"""
:type root: TreeNode
:type L: int
:type R: int
:rtype: int
"""
res = [0]
self.dfs(root, L, R, res)
return res[0]

def dfs(self, root, L, R, res):
if not root:
return
if L <= root.val <= R:
res[0] += root.val
if root.val < R:
self.dfs(root.right, L, R, res)
if root.val > L:
self.dfs(root.left, L, R, res)
``````

C++版本的代码如下：

``````/**
* 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 {
public:
int rangeSumBST(TreeNode* root, int L, int R) {
dfs(root, L, R);
return res;
}

private:
int res = 0;
void dfs(TreeNode* root, int L, int R) {
if (root == nullptr) return;
if (root->val <= R && root->val >= L) res += root->val;
if (root->val > L) dfs(root->left, L, R);
if (root->val < R) dfs(root->right, L, R);
}
};
``````

## # 日期

2018 年 11 月 11 日 —— 剁手节快乐 2018 年 12 月 2 日 —— 又到了周日