after 6 contest , the best i could do is around problem C or maybe B (yea im stupid :( ) i need some advice to improved my problem solving skill and some problems recommendations would help alot !!!

i have some issue when solving problem: + if i cant solve it under 10 minutes of thinking , im easily give up or use AI to give ideas + if i didnt encounter the same or similar technique in the past , it is hard for me to come up with a solution (or i will waste a ton of time just to prove mine thoughts is right or find the counter example + somehow , i have learnt some advance algorithm but i also lack of knowledge about easier algorithms

please help me