Gone Girl movie

One problem when one of your favorite books get adapted into a movie is that you already know how it’s going to end. Another problem is that 99% of the time, the book was better, but it’s always hard to cram the complexities of a novel into a 2-hour acted-out narrative. David Fincher and Gillian Flynn have circumvented the first problem by changing the ending of Gone Girl for the big screen. How much did they change?