HDU 5073 Galaxy

Test instructions is a given n point, which allows a point p to be found to minimize the Sigma ((A[i]-p) ^ 2), where A[i] represents the position of the point I. There are k points which don't count.

Idea: Found this problem is actually seeking n-k a point variance.

So push the formula:

Sigma ((A[i]-p) ^ 2)

= Sigma (a[i]^2 + p^2-2*a[i]*p)

= Sigma (a[i]^2 + p^2))-Sigma (2*a[i]*p)

= Sigma (a[i]^2) + (n-k) * (p^2)-2*p*sigma (A[i])//Because Sigma asks for the number of n-k and

= Sum2[i] + (n-k) * (p^2)-2*p*sum[i]

Here Sum2[i] is the sum of the preceding number of squares, sum[i] is the sum of the number of previous I. P is the average of this interval of length n-k. It can be obtained once the pretreatment. So the total time complexity is also O (n)

HDU 5073 Galaxy