I need help,
I'm on that task for a month and it's a shitty task where I need to write algorithms too complicated for my level and I'm totally demotivated right now... I can't even understand my own code and can't focus for more than 5min... I just wanna go home and never see that code and work on that anymore...
Has this situation ever happened to you ? What should I do ?

No joke, I sleep on it. The brain actually works on the problem when you're sleeping or napping and often I wake up with the answer.
Also if it's above your knowledge level, napping after learning something new helps cement that and you can put that knowledge to use when you wake up.

It might be time for you to take a break now.. 😴

Failing that, break down the bits you know and don't know and work through the process piece by piece rather than as a whole overwhelming jumbled function or whatever.

I can't help with the algo. The lack of focus happens nearly every day, especially when I'm stuck on something.

@badcopnodonuts
Well I guess the lack of sleep I have is certainly part of the problem :/ I'll try to sleep more this we to see if this will help for the next week.

Thank you for your help, I'll do what I can until the end of the day for now :)

@jeffalyanak
Thank you for that comment :)

Yeah some people told me the same, that the methodology of what to do is a big part of the work. So I'm starting a trello to keep track of my work ^^

Ask a colleague for help, and let your boss know that you need a little more support on the item.

What @jeffalyanak said.
I always have a private trello board, even when there is a trello board already, so I can create tasks as I need (no matter how stupid) to manage my own work.