POJ1905-Expanding Rods-二分答案
一根细棒升温时会变长,在两面墙中间,会变成一个弓形。
给出变长后的长度,求新的细棒中心与没伸长时的中心的距离。
简单的数学推导后就可以二分答案了,一开始没完全掌握二分的姿势,wa了好多。而且poj double输出要用%f,用%lf就wa了。
#include <cstdio> #include <cmath> #include <algorithm> using namespace std; const double eps = 1e-5; double n,c,L; double func(double x) { //if(fabs(x-0) < eps) return ; double r = (x*x+L*L/4.0)/(2*x); return 2*r*asin(L/(2.0*r)); } int main() { while(scanf("%lf%lf%lf",&L,&n,&c)) { if(L<0 && n<0 && c<0) break; double low = 0.0,high = 0.5*L; double mid = (low+high)/2.0; double s = (1+n*c)*L; double ans = 0; while(high-low>eps) { //printf("%lf %lf %lf\n",low,mid,high); //printf("%lf %lf %lf\n",func(low),func(mid),func(high)); if(func(mid) < s) low = mid; else high = mid; mid = (low+high)/2.0; } //printf("%f %f\n",mid,L); printf("%.3f\n",mid); } }