Convert Sorted List to Binary Search Tree - Leetcode

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; next = null; }
* }
*/
/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode sortedListToBST(ListNode head) {
if(head == null)
return null;

ListNode fast = head, slow = head, prev = slow;
if(head.next == null){
slow = head;
return new TreeNode(slow.val);
}
else if(head.next.next == null)  {
prev = slow;
slow = slow.next;
}else{
while(fast.next!=null && fast.next.next!=null){
prev = slow;
slow = slow.next;
fast = fast.next.next;
}
}
prev.next = null;
ListNode head2 = slow.next;
slow.next = null;

TreeNode root = new TreeNode(slow.val);
root.left = sortedListToBST(head);
root.right = sortedListToBST(head2);
return root;
}
}

分析：跟array 思路一样，然后因为是list，就用一个双速指针找到中值，然后及时切断前后连接。构造树。

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