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  • Dropping tests POJ

    In a certain course, you take n tests. If you get ai out of bi questions correct on test i, your cumulative average is defined to be

    .

    Given your test scores and a positive integer k, determine how high you can make your cumulative average if you are allowed to drop any k of your test scores.

    Suppose you take 3 tests with scores of 5/5, 0/1, and 2/6. Without dropping any tests, your cumulative average is . However, if you drop the third test, your cumulative average becomes .

    Input

    The input test file will contain multiple test cases, each containing exactly three lines. The first line contains two integers, 1 ≤ n ≤ 1000 and 0 ≤ k < n. The second line contains n integers indicating ai for all i. The third line contains n positive integers indicating bi for all i. It is guaranteed that 0 ≤ aibi ≤ 1, 000, 000, 000. The end-of-file is marked by a test case with n = k = 0 and should not be processed.

    Output

    For each test case, write a single line with the highest cumulative average possible after dropping k of the given test scores. The average should be rounded to the nearest integer.

    Sample Input

    3 1
    5 0 2
    5 1 6
    4 2
    1 2 7 9
    5 6 7 9
    0 0

    Sample Output

    83
    100

    Hint

    To avoid ambiguities due to rounding errors, the judge tests have been constructed so that all answers are at least 0.001 away from a decision boundary (i.e., you can assume that the average is never 83.4997).

    1.令F=Σ(a[i])/Σ(b[i]);

    2.令G=Σ(a[i])-F*Σ(b[i])=Σ(a[i]-F*(b[i]))

    3.当G>0时,存在更优的F;

    4.可以把a[i]-F*(b[i])看作每件商品对答案的贡献

     1 #include<iostream>
     2 #include<algorithm>
     3 #include<cmath>
     4 #include<cstdio>
     5 #include<cstring>
     6 using namespace std;
     7 
     8 int n,k;
     9 int a[1005],b[1005];
    10 double d[1005];
    11 
    12 bool check(double tem){
    13     double sum=0;
    14     for(int i=0;i<n;i++) d[i]=a[i]-tem*(b[i]);
    15     sort(d,d+n);
    16     for(int i=n-1;i>=k;i--) sum+=d[i];
    17     return sum>0 ? true:false;
    18 }
    19 
    20 void d_search(double ma){
    21     double l=0,r=ma;
    22     for(int i=0;i<100;i++){
    23         double mid=(l+r)/2.0;
    24         if(check(mid)) l=mid;
    25         else r=mid;
    26     }
    27     printf("%.0f
    ",l*100);
    28 }
    29 int main()
    30 {   while(~scanf("%d%d",&n,&k),n||k){
    31         32         for(int i=0;i<n;i++) scanf("%d",&a[i]);
    33         for(int i=0;i<n;i++) scanf("%d",&b[i]);
    34         d_search(1.0);
    35     }
    36     return 0;
    37 }
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  • 原文地址:https://www.cnblogs.com/zgglj-com/p/6836500.html
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