2015湘潭市第七届大学生程序设计竞赛 —— Fraction

题目大意：

　　小数化分数，但是分母限制在[1,1000],很明显的枚举，但是在赛场上的时候傻逼了，无论怎么枚举，怎么二分就是wa，wa到死···········。

（ps：我要给出题人寄刀片~~~~），这个题目需要注意的是有可能输出0/1.

 1 #include <cmath>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <iostream>
 5 #include <algorithm>
 6 using namespace std;
 7 const int maxn = 501000;
 8
 9 struct node
10 {
11     int x, y;
12 };
13 node stu[maxn];
14 bool cmp (node a, node b)
15 {
16     return a.x*1.0/a.y < b.x*1.0/b.y ? true : false;
17 }
18
19 int gcd (int a, int b)
20 {
21     return a%b==0?b:gcd(b, a%b);
22 }
23
24 int Bin_Sreach(double n, int low, int high)
25 {
26     while (low <= high)
27     {
28         int mid = (low + high) / 2;
29         double num = stu[mid].x * 1.0 / stu[mid].y;
30         if (num < n)
31             low = mid;
32         if (num > n)
33             high = mid;
34         if (high - low == 1)
35             break;
36     }
37     double num1 = stu[low].x*1.0 / stu[low].y;
38     double num2 = stu[high].x*1.0 / stu[high].y;
39     if (fabs(n - num1) > fabs(n - num2))
40         return high;
41     return low;
42 }
43 int main ()
44 {
45     int t, k = 1;
46
47     stu[0].y = 1;
48     for (int i=1; i<=1000; i++)
49         for (int j=i; j<=1000; j++)
50         {
51             if (gcd(j, i) == 1)
52             {
53                 stu[k].x = i;
54                 stu[k++].y = j;
55             }
56         }
57         sort (stu, stu+k, cmp);
58
59         scanf ("%d", &t);
60         while (t --)
61         {
62             double n;
63             scanf ("%lf", &n);
64             int p = Bin_Sreach(n, 0, k-1);
65             printf ("%d/%d\n", stu[p].x, stu[p].y);
66         }
67         return 0;
68 }