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

    private TreeNode createMidTree(int[] nums,int begin,int end)
    {
        if (begin>end) return null;
        int middle = (begin+end)/2;
        TreeNode node = new TreeNode(nums[middle]);
        node.left = createMidTree(nums,begin,middle-1);
        node.right = createMidTree(nums,middle+1,end);
        return node;
    }    
    
    public TreeNode sortedArrayToBST(int[] nums) {
        if(nums.length==0) return null;
        return createMidTree(nums,0,nums.length-1);
    }