HDU 2014 Anshan division 5073 galaxy

Meaning: give you n numbers, representing the positions of N planets. Each planet has a weight of 1!
At the beginning, every planet rotates around the center of gravity. The center of gravity is the sum of the positions of all planets/number of planets.
Now let you move K planets to any location (multiple planets can be in the same location and all planets are in the same straight line)
After moving, the locations of their centers may change, and the I = sum (di ^ 2) di (representing the distance from the first planet to the center of the center) is the smallest!

If D is the center of n-k planets, if the I value is the smallest, then the moving K planets must be placed in the hearts of the other n-k planets,
And the n-k planets must be continuous! The more intensive, the smaller the variance .....
X1, x2, X3, X4,... x (n-k) indicates the position of the remaining n-k planets
Thought: I = sum (di ^ 2) = (x1-d) ^ 2 + (x2-d) ^ 2 + (x3-d) ^ 2 ....
= Sum (Xi ^ 2) + (n-k) * D-2 * D * sum (XI );

1 # include <iostream> 2 # include <cstring> 3 # include <cstdio> 4 # include <algorithm> 5 # define n 50050 6 using namespace STD; 7 double num [N]; 8 double S1 [N], S2 [N]; 9 int main () {10 int N, T, K; 11 scanf ("% d", & T); 12 while (t --) {13 scanf ("% d", & N, & K ); 14 For (INT I = 1; I <= N; ++ I) 15 scanf ("% lf", & num [I]); 16 sort (Num + 1, num + n + 1); // rank 17 for the position of the planet (INT I = 1; I <= N; ++ I) // calculate the sum of the prefixes num [I] and the sum of num [I] ^ 2 and 18 S1 [I] = S1 [I-1] + num [I], s2 [I] = S2 [I-1] + num [I] * num [I]; 19 int M = n-k; 20 double ans = 1000000000000000000.0; // ans should be large enough .... it is better not to use long, which may exceed .... 21 For (INT I = 1; M & I + M-1 <= N; ++ I) {22 Int J = I + s-1; 23 double D = (S1 [J]-S1 [I-1])/m; 24 Double TMP = S2 [J]-S2 [I-1]-2 * D * (S1 [J]-S1 [I-1]) + M * D; 25 if (ANS> TMP) ans = TMP; 26} 27 if (n = k) ans = 0.0; 28 printf ("%. 9lf \ n ", ANS); 29} 30 return 0; 31}

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HDU 2014 Anshan division 5073 galaxy