三分 HDOJ 3714 Error Curves

 

题目传送门

 1 /*  2  三分：凹(凸)函数求极值  3 */  4 #include <cstdio>  5 #include <algorithm>  6 #include <cstring>  7 #include <cmath>  8 using namespace std;  9 10 const int MAXN = 1e4 + 10; 11 const int INF = 0x3f3f3f3f; 12 const double EPS = 0.0000000001; 13 struct F { 14 double a, b, c; 15 }f[MAXN]; 16 int n; 17 18 double cal(double x) { 19 double res = -INF; 20 for (int i=1; i<=n; ++i) { 21 res = max (res, f[i].a * x * x + f[i].b * x + f[i].c); 22  } 23 return res; 24 } 25 26 int main(void) { //HDOJ 3714 Error Curves 27 //freopen ("HDOJ_3714.in", "r", stdin); 28 29 int T; scanf ("%d", &T); 30 while (T--) { 31 scanf ("%d", &n); 32 for (int i=1; i<=n; ++i) { 33 scanf ("%lf%lf%lf", &f[i].a, &f[i].b, &f[i].c); 34  } 35 36 double l = 0.0, r = 1000.0; 37 for (int i=1; i<=100; ++i) { 38 double mid = (l + r) / 2; 39 double rmid = (mid + r) / 2; 40 if (cal (mid) < cal (rmid)) r = rmid; 41 else l = mid; 42  } 43 printf ("%.4f\n", cal (r)); 44  } 45 46 return 0; 47 }