Strange fuction
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3344 Accepted Submission(s): 2446
Problem Description
Now, here is a fuction:
F(x) = 6 * x^7+8*x^6+7*x^3+5*x^2-y*x (0 <= x <=100)
Can you find the minimum value when x is between 0 and 100.
Input
The first line of the input contains an integer T(1<=T<=100) which means the number of test cases. Then T lines follow, each line has only one real numbers Y.(0 < Y <1e10)
Output
Just the minimum value (accurate up to 4 decimal places),when x is between 0 and 100.
Sample Input
2 100 200
Sample Output
-74.4291 -178.8534
Author
Redow
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对这个函数连续求几次导可以发现,对于此函数的导函数,如果y <= 0,那么函数在[0, 100]内单调递增,所以最小值是0
如果y>0,观察其导函数,发现导函数单调递增,所以我们只要找到导函数的零点(即原函数的极小值点),此时可以用二分解决
找到极值点以后,如果它在[0, 100],就把它代入函数,否则说明函数在[0, 100]内单调递减,把100代入函数即可
#include <map> #include <set> #include <list> #include <stack> #include <queue> #include <vector> #include <cmath> #include <cstdio> #include <cstring> #include <iostream> #include <algorithm> using namespace std; int main() { int t; scanf("%d\n", &t); while (t--) { double y; scanf("%lf", &y); if (y <= 0) { printf("0.0000\n"); continue; } double l = 0, r = 100, mid; while(r - l > 1e-6) { mid = (l + r) / 2; double dx = 42.0 * pow(mid, 6) + 48.0 * pow(mid, 5) + 21.0 * pow(mid, 2) + 10.0 * mid; if (abs(dx - y) < 1e-6) { break; } else if(dx - y > 1e-6) { r = mid; } else { l = mid; } } if (mid - 100.0 > 1e-6) { mid = 100.0; } double ans = 6 * pow(mid, 7) + 8 * pow(mid, 6) + 7 * pow(mid, 3) + 5 * pow(mid, 2) - y * mid; printf("%.4f\n", ans); } return 0; }