CF1130E Wrong Answer

Posted 2021-02-14 huangchenyan

构造题+数学

题意是要求一个序列中最大的∑(i>=l且i<=r) (r-l+1)*a[i]的值，题目给出代码，要你hack这份代码，使他的答案与正确答案相差k

function find_answer(n, a)
    # Assumes n is an integer between 1 and 2000, inclusive
    # Assumes a is a list containing n integers: a[0], a[1], ..., a[n-1]
    res = 0
    cur = 0
    k = -1
    for i = 0 to i = n-1
        cur = cur + a[i]
        if cur < 0
            cur = 0
            k = i
        res = max(res, (i-k)*cur)
    return res

考虑在第一个数放一个负数-1，之后的1999个数之和为sum，

则他代码的答案为 sum*1999

正确答案为 (sum-1)*2000

所以 (sum-1)*2000-sum*1999=k

化简得 sum=k+2000

之后将sum均分个之后的1999个数即可

 

#include <bits/stdc++.h>
using namespace std;
int k,sum;
int main()
{
    scanf("%d",&k);
    sum=k+2000;
    printf("2000
");
    int t,h;
    t=sum/1998;
    h=sum-1998*t;
    printf("-1 ");
    for (int i=1;i<=1998;i++)
      printf("%d ",t);
    printf("%d
",h);
}