public Node deleteNode(Node deleteNode, Node parentNode){
		if(deleteNode.getLeft() == null && deleteNode.getRight() == null) return null;
		else if(deleteNode.getLeft() == null && deleteNode.getRight() != null) return deleteNode.getRight();
		else if(deleteNode.getLeft() != null && deleteNode.getRight() == null) return deleteNode.getLeft();
		
		else {
			// 오른쪽 Node에서 제일 작은 Node
			Node temp = deleteNode.getRight();
			while(temp.getLeft() != null){
				parentNode = temp;
				temp = temp.getLeft();
			}
			
			deleteNode.setKey(temp.getKey());
			
			if(temp.getKey() == deleteNode.getRight().getKey()) deleteNode.setRight(temp.getRight());
			else parentNode.setLeft(temp.getRight());
			
			return deleteNode;
		}
	}