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80 lines
1.8 KiB
Markdown
80 lines
1.8 KiB
Markdown
# [938. Range Sum of BST](https://leetcode.com/problems/range-sum-of-bst/)
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## 题目
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Given the `root` node of a binary search tree, return *the sum of values of all nodes with a value in the range `[low, high]`*.
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**Example 1:**
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```
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Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
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Output: 32
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```
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**Example 2:**
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```
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Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
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Output: 23
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```
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**Constraints:**
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- The number of nodes in the tree is in the range `[1, 2 * 10^4]`.
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- `1 <= Node.val <= 10^5`
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- `1 <= low <= high <= 10^5`
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- All `Node.val` are **unique**.
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## 题目大意
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给定二叉搜索树的根结点 root，返回值位于范围 [low, high] 之间的所有结点的值的和。
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## 解题思路
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- 简单题。因为二叉搜索树的有序性，先序遍历即为有序。遍历过程中判断节点值是否位于区间范围内，在区间内就累加，不在区间内节点就不管。最终输出累加和。
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## 代码
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```go
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package leetcode
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import (
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"github.com/halfrost/LeetCode-Go/structures"
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)
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// TreeNode define
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type TreeNode = structures.TreeNode
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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func rangeSumBST(root *TreeNode, low int, high int) int {
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res := 0
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preOrder(root, low, high, &res)
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return res
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}
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func preOrder(root *TreeNode, low, high int, res *int) {
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if root == nil {
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return
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}
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if low <= root.Val && root.Val <= high {
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*res += root.Val
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}
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preOrder(root.Left, low, high, res)
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preOrder(root.Right, low, high, res)
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}
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``` |