108. Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

题目含义：给定了一个升序的数组，转换成一个平衡二叉树

 1     private TreeNode createMidTree(int[] nums,int begin,int end)
 2     {
 3         if (begin>end) return null;
 4         int middle = (begin+end)/2;
 5         TreeNode node = new TreeNode(nums[middle]);
 6         node.left = createMidTree(nums,begin,middle-1);
 7         node.right = createMidTree(nums,middle+1,end);
 8         return node;
 9     }    
10     
11     public TreeNode sortedArrayToBST(int[] nums) {
12         if(nums.length==0) return null;
13         return createMidTree(nums,0,nums.length-1);
14     }