Code challenges

Hey! I'm recently doing some code challenges in interviews to get a job remotly.

In those challenges sometimes I can't reach the minimum points to procced to the next step. So when I see a code that doens't performs well or is badly written, I really want to find what is wrong and try to improve it. But sadly is very hard to find those challenges solved, specially with PHP.

So I came here to ask if someone knows a nice website to train challenges, and most important, if that place shows the challenge solved to compare with my code.