leetcode

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938. Range Sum of BST

题目

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].

Example 1:

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

Example 2:

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

Constraints:

• The number of nodes in the tree is in the range [1, 2 * 10^4].
• 1 <= Node.val <= 10^5
• 1 <= low <= high <= 10^5
• All Node.val are unique.

题目大意

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。

解题思路

• 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。

代码

package leetcode

import (
	"github.com/halfrost/LeetCode-Go/structures"
)

// TreeNode define
type TreeNode = structures.TreeNode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

func rangeSumBST(root *TreeNode, low int, high int) int {
	res := 0
	preOrder(root, low, high, &res)
	return res
}

func preOrder(root *TreeNode, low, high int, res *int) {
	if root == nil {
		return
	}
	if low <= root.Val && root.Val <= high {
		*res += root.Val
	}
	preOrder(root.Left, low, high, res)
	preOrder(root.Right, low, high, res)
}

Documentation

Index

• type TreeNode

Types

type TreeNode

type TreeNode = structures.TreeNode

TreeNode define