HDU 4355-三分

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http://acm.hdu.edu.cn/showproblem.php?pid=4355

题目给n个人的位置和权值w

选数轴上一实数点，求每个人到该点的距离dis的三次方*w，的和

让这个和最小。

分析得，为单峰函数，三分解决

#include <cstdio>#include <cmath>#include <cstring>#include <string>#include <algorithm>#include <queue>#include <map>#include <set>#include <vector>#include <iostream>//#include <time.h>using namespace std;const double pi=acos(-1.0);double eps=0.000001;struct node{    double x,w;    node() {}    node( double a,double b)    {        x=a,w=b;    }};node aa[50005];        int n;double F(double pos){    double   ans=0;    for (int i=1; i<=n; i++)    {        double sb=fabs(aa[i].x-pos);        ans+=sb*sb*sb*aa[i].w;    }    return ans;}//double aaa[10005];int main(){    int t;    cin>>t;  //  srand( (unsigned)time( NULL ) );int cnt=1;    while(t--)    {        cin>>n;        double x,w;        int i;     /*   for (i=1;i<=n;i++)        aaa[i]=rand()%1000*1.5;*/        //sort(aaa+1,aaa+1+n);        for (i=1; i<=n; i++)        {            scanf("%lf %lf",&aa[i].x,&aa[i].w);           // aa[i].x=aaa[i]*pow(-1.0,1.0*i);           // aa[i].w=rand()%15*1.0;        }        double l=-1e6;        double r=1e6;      for (i=0;i<100;i++)        {            double m1=l+(r-l)/3;            double m2=r-(r-l)/3;            if (F(m2)>F(m1))                r=m2;            else                l=m1;        }        printf("Case #%d: %.0lf\n",cnt++,F(l));/*        double minn=F(1);        for (i=1;i<=n;i++)        {            minn= min(minn,F(i));        }        long long oo=(long long) (minn);        printf("ans2::%lld\n",oo);*/    }    return 0;}

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