[Codevs1283] equidifference subsequence (Binary)

Title: http://codevs.cn/problem/1283/

Analysis:

It mainly saves time on each decision. The general practice is to open an array to record the appearance of each number, and then each time you read a number, it will be extended to both sides in the middle until the two symmetric pointers point to the number. In fact, this is a full arrangement. Therefore, if one of the numbers on the left of X appears and the corresponding right position is meaningful, the right position will certainly appear later. Therefore, this greatly saves time.

[Codevs1283] equidifference subsequence (Binary)