Convert Sorted List to Binary Search Tree

Convert Sorted List to Binary Search Tree

问题：

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

思路：

　　典型的dfs思路

我的代码：

public class Solution {
public TreeNode sortedListToBST(ListNode head) {
if(head == null)    return null;
if(head.next == null) return new TreeNode(head.val);
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode mid = getMiddle(head, dummy);
TreeNode root = new TreeNode(mid.val);
TreeNode left = sortedListToBST(dummy.next);
TreeNode right = sortedListToBST(mid.next);
root.left = left;
root.right = right;
return root;
}
public ListNode getMiddle(ListNode head, ListNode dummy)
{
ListNode pre = dummy;
ListNode slow = head;
ListNode fast = head.next;
while(fast != null && fast.next != null)
{
slow = slow.next;
fast = fast.next.next;
pre = pre.next;
}
pre.next = null;
return slow;
}
}

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