题解 | #将升序数组转化为平衡二叉搜索树#

这道题的难点就在于是否能够发现其实每次都需要将下中位点拿来做根节点,hhh

    public TreeNode sortedArrayToBST (int[] num) {
        if(num==null||num.length==0) return null;
        return createBST(num,0,num.length-1);
    }
    public TreeNode createBST(int[] num,int start,int end){
        if(start>end){
            return null;
        }
        int mid = (end+start+1)>>1;//这个+1是精髓
        TreeNode head = new TreeNode(num[mid]);
        TreeNode left = createBST(num,start,mid-1);
        TreeNode right = createBST(num,mid+1,end);
        head.left = left;
        head.right = right;
        return head;
    }