I have come across two problems but could not build the logic to implement them.

Question 1:

given an array a of n elements [a1,a2,a3,...,an]. To calculate f(i) first sorting elements from 1 to i in non-decreasing order, then use the formula f(i)= =(1*a[1])+(2*a[2])+(3*a[3])+..+(i*a[i]). Compute (f(1)+f(2)+f(3)+...+f(n))mod(10^9+7).

constraints: 1<=n<=10^5

1<=a[i]<=10^6

Sample case: a[]=[4,3,2,1] output:65

explanation:

f(1)=1*4=4 f(2)=1*3+2*4=11 f(3)=1*2+2*3+3*4=20 f(4)=1*1+2*2+3*3+4*4=30

so output is 65%(10^9+7)=65.

Question 2:

Given an array a of n elements [a0,a1,a2,...an-1]. The value of array is defined square of sum of even positioned elements minus odd positioned elements. Find the maximum possible value of any subarray of a[].

constraints: 1<=n<=10^5

-10^6<=a[i]<=10^6

sample case: a[]=[-1,-4,2] output: 36

explanation: consider the subarray[-4,2] the value is(-4-2)^2=36.

Hi Codeforces,

As the title suggests, I tried building the dynamic version of all time favorite A2oj ladders. The site contains all ladders of A2oj even the extra ones. In addition to A2oj ladders, I have also added questions in the form of ladders from Specialist Sheet and Expert Sheet made by kartik8800, as these questions are comparatively newer.

Here is the link to the site: Dynamic A2oj

Hope you all like it.

Happy Programming!!!.