A. plank
label:
Prime factors specific root sign 筛法
answer:
Can be obtained by the similar triangles:
$ ans=8*\sum_{i=1}^{n-1}[i*i(mod)n==0] $
Root prime factors to screen out
B. cleaning
label:
Dp + list
Correct answer:
A violence can be a question, but the solution is not hard to think positive
The most violent Dp formula: $ f [i] = min {f [j] + cnt (j + 1, i) ^ 2} $
If j i-1 from the enumeration, we found that when cnt number to more than sqrt (f [i]) after the answer must not contribute
Consider maintaining a list with each number as of the end position i appear to ensure that the complexity of $ O (nsqrt (n)) $