题目传送门
1 /*
2 二分搜索：式子两边取对数，将x提出来，那么另一边就是一个常数了，函数是：lnx/x。二分搜索x，注意要两次
3 */
4 #include <cstdio>
5 #include <algorithm>
6 #include <cmath>
7 using namespace std;
8
9 const double e = exp (1.0);
10
11 double cal(double x) {
12 return log (x) / x;
13 }
14
15 int main(void) { //HDOJ 2675 Equation Again
16 //freopen ("HDOJ_2675.in", "r", stdin);
17
18 double y, k;
19 while (scanf ("%lf", &y) == 1) {
20 k = (1 + log (y)) / (e * y);
21 //if (k > 1 / e) { //囧！
22 // puts ("Happy to Women’s day!"); continue;
23 //}
24 if (k == 1 / e) {
25 printf ("%.5f
", e); continue;
26 }
27
28 double x1, x2;
29 double l = 0, r = e;
30 for (int i=1; i<=100; ++i) {
31 double mid = (l + r) / 2;
32 if (cal (mid) >= k) r = mid;
33 else l = mid;
34 }
35 x1 = l;
36 l = e, r = 1e9;
37 for (int i=1; i<=100; ++i) {
38 double mid = (l + r) / 2;
39 if (cal (mid) >= k) l = mid;
40 else r = mid;
41 }
42 x2 = l;
43 printf ("%.5f %.5f
", x1, x2);
44 }
45
46 return 0;
47 }