[leetcode]109 Convert Sorted List to Binary Search Tree

https://oj.leetcode.com/problems/convert-sorted-list-to-binary-search-tree/

Http://fisherlei.blogspot.com/2013/01/leetcode-convert-sorted-list-to-binary.html

http://blog.csdn.net/worldwindjp/article/details/39722643

/** * 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)  {                 // option  A:        treenode root = buildtop2buttom (head,  NULL);        return root;    }     //////////////////////////    // Option A: Top to  bottom    //    // unlike sorted array, no  random access.    // but we still can follow the  Same strategy that:    // given head, find the mid.     // o (n log n)     private TreeNode  Buildtop2buttom (listnode start, listnode end)     {         if  (start == null | |  start == end)             return null;                     if  (start.next == end)              return new treenode (Start.val);                 listnode mid =  findmid (start, end);        treenode root =  New treenode (Mid.val);        root.left =  Buildtop2buttom (Start, mid);        root.right =  Buildtop2buttom (mid.next, end);        return root;     }        // find the mid node  from  ' start ' (inclusive)  TO  ' End ' (exclusive)     private listnode findmid (Listnode start, listnode  end)     {        listnode toreturn  = null;        ListNode s1 = start;         ListNode s2 = start;         while  (s2 != null && s2 != end)          {             toreturn = s1;            s1 =  s1.next;            s2 = s2.next;             if  (s2 == null | |  s2 == end)             s2 = null;             else             s2 = s2.next;        }         return toreturn;    }}

[leetcode]109 Convert Sorted List to Binary Search Tree