public static TreeNode buildTree1(int[] preorder, int[] inorder) {
		// write your code here
		Map<Integer,Integer>map=new HashMap<>();
		int[]A=preorder, B=inorder;
		for (int i=0;i<B.length;++i)
			map.put(B[i],i);
		return btHelper(A,0,A.length,0,A.length,map);
	}