Summary of these days

I have learned from these questions and competitions over the past few days, but I am not sure I want to knock on the code at will. It is even more confusing to knock on the wrong code than to knock on the code, sometimes it takes enough time to get a tiny error to rewrite the code several times. When writing code, you must be careful. A "probably like this" may destroy more than N times behind you. Do not believe that the question says that there is only one set of test data. If the algorithm is changed, it means that a cannot be lost. No matter whether the variables are clear or not, there are no multiple groups of data, but that is certainly true. (PS: I 'd better click on the problem and see how many amazing mistakes can be made)