POJ-2976 Dropping tests---二分最大化平均值

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cmath>
 5 #include<cstring>
 6 using namespace std;
 7 typedef long long ll;
 8 const int maxn = 1e3 + 10;
 9 int n, k;
10 int a[maxn], b[maxn];
11 double c[maxn];
12 bool judge(double x)
13 {
14     for(int i = 0; i < n; i++)
15         c[i] = a[i] - x * b[i];
16     sort(c, c + n);
17     double sum = 0;
18     for(int i = 0, j = n - 1; i < k; i++, j--)//前k个大的数
19         sum += c[j];
20     return sum >= 0;
21 }
22 int main()
23 {
24     while(cin >> n >> k && n)
25     {
26         for(int i = 0; i < n; i++)scanf("%d", &a[i]);
27         for(int i = 0; i < n; i++)scanf("%d", &b[i]);
28         k = n - k;
29         double l = 0, r = 1;
30         for(int i = 0; i < 50; i++)
31         {
32             double mid = (l + r) / 2;
33             if(judge(mid))l = mid;
34             else r = mid;
35         }
36         printf("%.f\n", 100 * l);
37     }
38     return 0;
39 }