题目：

题解：

var globalHead *ListNode

func sortedListToBST(head *ListNode) *TreeNode {
    globalHead = head
    length := getLength(head)
    return buildTree(0, length - 1)
}

func getLength(head *ListNode) int {
    ret := 0
    for ; head != nil; head = head.Next {
        ret++
    }
    return ret
}

func buildTree(left, right int) *TreeNode {
    if left > right {
        return nil
    }
    mid := (left + right + 1) / 2
    root := &TreeNode{}
    root.Left = buildTree(left, mid - 1)
    root.Val = globalHead.Val
    globalHead = globalHead.Next
    root.Right = buildTree(mid + 1, right)
    return root
}