poj2507 Crossed ladders

题意：
已知x,y,c,求d
题解：答案满足单调性，即x，y恒定时，d越大，c越小。因此可以二分答案。

#include<cstdio>#include<cmath>#include<algorithm>using namespace std;#define eps 1e-5double l,r,mid,a,b,c,x,y,now;bool judge(double k){    x=sqrt(a*a-k*k);    y=sqrt(b*b-k*k);    now=(x*y)/(x+y);    if(now-c>eps) return 0;    else return 1;}int main(){    while(scanf("%lf%lf%lf",&a,&b,&c)!=EOF){        l=0;r=max(a,b);        while(r-l>=eps){            mid=(l+r)/2.0;            if(judge(mid)) r=mid;            else l=mid;        }        printf("%.3lf\n",l);    }    return 0;}