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  • HDU2899 Strange fuction 【二分】

    Strange fuction

    Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
    Total Submission(s): 2982    Accepted Submission(s): 2202


    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
     


    #include <stdio.h>
    #include <math.h>
    double y, ans;
    
    double f(double x){
    	return 6 * pow(x, 7) + 8 * pow(x, 6) + 
    		7 * pow(x, 3) + 5 * x * x - y * x;
    }
    
    double ff(double x){ //求导
    	return 42 * pow(x, 6) + 48 * pow(x, 5) 
    		+ 21 * x * x + 10 * x - y;
    }
    
    int main(){
    	int n;
    	scanf("%d", &n);
    	while(n--){
    		scanf("%lf", &y);
    		if(ff(0) >= 0) ans = f(0);
    		else if(ff(100) <= 0) ans = f(100);
    		else{
    			double left = 0, right = 100, mid;
    			while(left + 1e-8 < right){
    				mid = (left + right) / 2;
    				if(ff(mid) > 0) right = mid;
    				else if(ff(mid) < 0) left = mid;
    				else break;
    			}
    			ans = f(mid);
    		}
    		printf("%.4lf
    ", ans);
    	}
    	return 0;
    }


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  • 原文地址:https://www.cnblogs.com/yxysuanfa/p/6956352.html
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