三分

HihoCoder - 1142一道三分题。

 

以前只接触过二分，现在才接触的三分，刚接触的时候感觉有点陌生。

 

我们只要理解三分的意思即可做出这道题

 

 

 

#include<set>
#include<map>
#include<queue>
#include<stack>
#include<bitset>
#include<math.h>
#include<string>
#include<vector>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define pi acos(-1)
#define close ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
using namespace std;
typedef long long ll;
const int MAX_N=1000000+50;
const int INF=0x3f3f3f3f;
const double EPS = 1e-9;
ll mod = 1e9+7;

double a,b,c,x,y;

double dis(double x1,double y1,double x2,double y2){
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}

//计算距离
double Calc(double xx){
	double yy = a*xx*xx+b*xx+c;
	return dis(xx,yy,x,y);
} 

//三分
double Solve(){
	double Left,Right;
	double mid,midmid;
	double mid_value,midmid_value;
	Left = -200;Right = 200;
	while(Left + EPS < Right){
		mid = (Left + Right) / 2.0;
		midmid = (mid + Right) / 2.0;
		mid_value = Calc(mid);
		midmid_value = Calc(midmid);
		
		if(mid_value < midmid_value) Right = midmid;
		else Left = mid;
	}
	return midmid_value;
} 

int main(){
	while(~scanf("%lf %lf %lf %lf %lf",&a,&b,&c,&x,&y)){
		printf("%.3lf\n",Solve());
	}	
 	return 0;
}

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