Summary of NOIP2015 Popularization Group
The overall feeling of this exam is good, but I feel that the time is a little tight, and it was finished in the last 30 minutes.
The first question (gold coins): Big W! Explosive search O(N), finished in one minute;
the second question (minesweeper game): same as above;
the third question (sum): This question is not difficult, but it also stuck me for 15 minutes. Factorize the answers with the same color and the same remainder after dividing by 2 in each group that meets the conditions (fortunately, I recently learned (è)xi (bǔ) factorization) and then find the rules, O(2N );
Question 4 (salesman salesman): This question is not too difficult, but I have not been able to think of a correct solution, so it took me half an hour. Just when I was about to lose confidence, the funny little student sitting next to me (note: it was a primary school student) suddenly said to himself: "I'm right on the fourth question!" (Actually, I later learned from his self-talk I learned that it was not the correct solution...), and then I was stunned! ! ! I thought: Even elementary school students have typed the correct solution, can't I get it yet...#￥%&. So I was refreshed and full of confidence! ! ! Then I thought of a big water method that 95% of the time can get stuck (praise! (sweat!)), and then I hit it. . . Time complexity O(NmaxAi).
This time the harvest is very big, that is: when you encounter problems that you can't solve, think hard about the water method! ! !