public static Node getMaxTree(int[] arr){
		Node[] nArr=new Node[arr.length];
		for(int i=0;i!=arr.length;i++){
			nArr[i]=new Node(arr[i]);
		}
		Stack<Node> stack=new Stack<Node>();
		Map<Node,Node> lBigMap=new HashMap<Node,Node>();
		Map<Node,Node> rBigMap=new HashMap<Node,Node>();
		for(int i=0;i!=nArr.length;i++){
			Node curNode=nArr[i];
			while(!stack.isEmpty()&&stack.peek().value<curNode.value){
				popStackSetMap(stack,lBigMap,rBigMap,curNode);
			}
			stack.push(curNode);
		}
		while(!stack.isEmpty()){
			popStackSetMap(stack,lBigMap,rBigMap,null);
		}
		Node head =null;
		for(int i=0;i!=nArr.length;i++){
			Node curNode=nArr[i];
			Node left=lBigMap.get(curNode);
			Node right=rBigMap.get(curNode);
			if(left==null&&right==null){
				head=curNode;
			}else if(left==null){
				if(right.left==null){
					right.left=curNode;
				}else{
					right.right=curNode;
				}
			}else if(right==null){
				if(left.left==null){
					left.left=curNode;
				}else{
					left.right=curNode;
				}
			}else{
				Node parent =left.value<right.value?left:right;
				if(parent.left==null){
					parent.left=curNode;
				}else{
					parent.right=curNode;
				}
			}
		}
		return head;
	}
	public static void popStackSetMap(Stack<Node> stack,Map<Node,Node> lmap,Map<Node,Node> rmap,Node curNode){
		Node popNode=stack.pop();
		if(stack.isEmpty()){
			lmap.put(popNode,null);
		}else{
			lmap.put(popNode, stack.peek());		
		}
		rmap.put(popNode, curNode);
	}

第4题改进版