规律杂记

geometry

• You are given 2n points, you need to pair them to create n rectangles so that the intersection of all those rectangles forms a positive area. In how many ways you can do that?
• answer: The intersection area of the rectangles is always the same if the area is positive. sort $x_i$ $and$ $y_i$ , calculate the number of points below and up the $(x_n,y_n)$ and $(x_{n+1},y_{n+1})$ points, and the answer is $a!\ast b!$

permutation

string

• count the number of different S with the minimum number of distinct palindromic substring.
• as the $|S|$ range in $[1,1e9]$ so we should find the minimum number in a small range ,and we can find that

   if(n == 1) printf("26\n");
   if(n == 2) printf("676\n");
   if(n == 3) printf("17576\n");
   else printf("15600\n");