HDU 5073 galaxy Accuracy

 

Idea: in fact, the solution is very simple. If we move K numbers and then the upper and lower degrees have the smallest angular momentum, it must be connected (n-k). As for why do you Think About It (easy );

For some mass point centers in the location and the number of points divided

Average = sum [l, l + (n-k)-1]/(n-k );

Value of one vertex: (Pi-average) * (Pi-average)

That is, PI ^ 2 + Avery ^ 2-2 * pI * Average

Add multiple vertices, that is, Σ PI ^ 2 + (n-k) * sum/(n-k) -2 * Σ pI * sum/(n-k );

= Σ PI ^ 2 + (n-k) * sum/(n-k)-2 * sum/(n-k );

= Σ PI ^ 2-sum * sum/(n-k );

So we need to deal with "common" and "sum of squares ".

However, this card accuracy: My practice is to compare (n-k) * Σ PI ^ 2-sum * sum

Just divide the smallest value by (n-k ).

Code. cpp

 

 1 #include <string> 2 #include <cstring> 3 #include <iostream> 4 #include <cstdio> 5 #include <algorithm> 6 using namespace std; 7 typedef long long ll; 8 int n,k,d[50005]; 9 ll sum[50005];10 ll getsum(int i,int j)11 {12     if(i)return sum[j-1]-sum[i-1];13     else return sum[j-1];14 }15 16 int main()17 {18     int t;19     scanf("%d",&t);20     while(t--)21     {22         memset(d,0,sizeof d);23         memset(sum,0,sizeof sum);24         scanf("%d%d",&n,&k);25         for(int i=0;i<n;i++)26             scanf("%d",&d[i]);27         sort(d,d+n);28         for(int i=0;i<n;i++)29             if(i) sum[i]=sum[i-1]+(ll)d[i];30             else sum[i]=(ll)d[i];31         double messc=0.0,minv=0.0,now=0.0;32         for(int j=0;j<=k;j++)33         {34             ll nows=getsum(j,n-(k-j));35             messc=(double)nows/(double)(n-k);36             now=0.0;37             for(int i=j;i<=(n-1)-(k-j);i++)38             {39                 double dis=(double)d[i]-messc;40                 now+=(dis*dis);41                 if(j && now>=minv) break;42             }43             if(!j)minv=now;44             else if(now<minv) minv=now;45         }46         printf("%.12f\n",minv);47     }48     return 0;49 }

 

HDU 5073 galaxy Accuracy