ConvertSortedArrToBST.java

    //RECURSIVE
    public TreeNode sortedArrayToBSTRecursive(int[] nums) {
        if(nums == null)return null;

        TreeNode root = sortedArrayToBSTHelper(nums,0,nums.length-1);

        return root;
    }

    public TreeNode sortedArrayToBSTHelper(int[] nums, int begin, int end) {
        if(nums == null)return null;
        if(begin > end) return null;

        int mid = (begin + end)/2;
        TreeNode root = new TreeNode(nums[mid]);
        root.left=sortedArrayToBSTHelper(nums, begin, mid-1);
        root.right=sortedArrayToBSTHelper(nums,mid+1, end);
        return root;
    }