938. 二叉搜索树的范围和

package main
import "fmt"
type TreeNode struct {
         Val int
         Left *TreeNode
         Right *TreeNode
 }
 //
func rangeSumBST(root *TreeNode, L int, R int) int {
    stack := make([]*TreeNode,0)
    var res =0
    for root!=nil||len(stack)>0{
        for root!=nil{
            stack = append(stack,root)
            root = root.Left
        }
        node :=stack[len(stack)-1]
        stack =stack[:len(stack)-1]
         if node.Val>=L&&node.Val<=R{
            res +=node.Val
            if node.Val==R{
                return res
            }
        }
        root = node.Right
    }
    return res
}
func main() {
    ten :=&TreeNode{Val:10}
    five :=&TreeNode{Val:5}
    ten.Left = five
    fifteen :=&TreeNode{Val:15}
    ten.Right = fifteen
    three :=&TreeNode{Val:3}
    five.Left = three
    seven :=&TreeNode{Val:7}
    five.Right = seven
    eighteen :=&TreeNode{Val:18}
    fifteen.Right = eighteen
    fmt.Println(rangeSumBST(ten,7,15))
}