How does mersault pass the time in prison?

Mersault diverted his mind in memorizing the things in his room, deep into the finer details until he no longer feels bored.

Explanation:

Albert Camus' "The Stranger" tells the story of our narrator/ protagonist who was convicted of murder for killing an Arab. The whole story dwells on the theme of existentialism and the very identity of an individual.

The speaker had just been jailed for the death of the Arab, though that wasn't the only reason he was convicted. After looking at his reactions during his mother's death, his behavior towards his girlfriend and others, including his admittance that he doesn't particularly believe in God, all contributed to his fate. While in prison, he finds it hard at first, to comply to the life of imprisonment. But then gradually, he began to have "prisoner’s thoughts", thinking about his time in prison and how to pass the time. He began to memorize his room, "starting from a corner, make the round, noting  every object I saw on the way visualizing every  piece of furniture, and each article upon or in it, and then every detail of each article and finally the details of the details, so to speak: a tiny dent or incrustation, or a  chipped edge, and the exact grain and color of the woodwork".

This eventually took up all of his time, keeping him occupied. He admitted "after a few weeks, I could spend hours  merely in listing the objects in my bedroom. I found that the more I thought, the  more details, half-forgotten or mal-observed, floated up from my memory. There  seemed no end to them".  In this way, he passed his time in the prison.

alone =having no one else present.