For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
"Hills Like White Elephants" is a revolutionary approach to story writing, and perhaps even a reaction against stories that fit into traditional plot structures. As a result, this story cannot be broken into three acts.