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/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

/**

* Definition for a binary tree node.

* 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;

if(head.next == null) return new TreeNode(head.val);

ListNode slow = head;

ListNode fast = head;

ListNode preSlow = head;

while(fast!=null && fast.next!=null){

preSlow = slow;

slow = slow.next;

fast = fast.next.next;

}

ListNode second = slow.next;

preSlow.next = null;

ListNode first = head;

TreeNode root = new TreeNode(slow.val);

root.left = sortedListToBST(first);

root.right = sortedListToBST(second);

return root;

}

}