Rolling Variance

The input contains at most 30 sets. For each set:

The first line contains 2 integers n,m (2≤m≤n≤105).

The second line contains n integers a1,a2,…,an (|ai|≤100).

For each set, (n−m+1) lines with floating numbers r1,r2,…,rn−m+1.

Your answer will be considered correct if its absolute or relative error does not exceed 10−4.

3 2
1 3 2
5 3
1 3 2 4 5

1.41421356
0.70710678
1.00000000
1.00000000
1.52752523

Main(A,n,m)：
For i=1 to n-m+1
Sub_ Sum = 0
For j=i to i+m-1
Sub_ Sum = Sub_ Sum + A[j]
Average =Sub_ Sum /m
Sub_denom = 0
For j=I to i+m-1
Sub_denom = Sub_denom + (A[j]-Average)^2
Print sqrt[Sub_denom/(m-1)]

Main(A,n,m)
Array Sub_Sum[n-m+1],Sub_Ave [n-m+1],Sub_Quasum [n-m+1]
Sub_Sum[1]=0
Sub_Quasum [1]=0
For i=1 to m
Sub_Sum[1] = Sub_Sum[1] + A[i]
Sub_Quasum [1] = Sub_Quasum [1] + A[i]*A[i]
Sub_Ave[1] = Sub_Sum[1]/m
For j=2 to n-m+1
Sub_Sum[j] = Sub_Sum[j] – A[j-1] + A[j+m-1]
Sub_Quasum [j] = Sub_Quasum [j] – A[j-1]*A[j-1] + A[j-m+1]*A[j-m+1]
Sub_Ave[j] = Sub_Sum[j]/m
For i=1 to n-m+1
ans=Sub_Quasum [i]–2*Sub_Ave[i]* Sub_Sum[i]+m*Sub_Ave[i]* Sub_Ave[i]
ans/m-1
Print sqrt(ans)
//但是比赛时各种RE，最后把数组开到了 2.5*10^5 （题目数据范围的2倍）才过，也不知道是不是题目数据大了