hdu5753Permutation Bo+数学期望
2016-07-26 20:54
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Problem Description
There are two sequences h1∼hn and c1∼cn. h1∼hn is a permutation of 1∼n. particularly, h0=hn+1=0.
We define the expression [condition] is 1 when condition is True,is 0 when condition is False.
Define the function f(h)=∑ni=1ci[hi>hi−1 and hi>hi+1]
Bo have gotten the value of c1∼cn, and he wants to know the expected value of f(h).
Input
This problem has multi test cases(no more than 12).
For each test case, the first line contains a non-negative integer n(1≤n≤1000), second line contains n non-negative integer ci(0≤ci≤1000).
Output
For each test cases print a decimal - the expectation of f(h).
If the absolute error between your answer and the standard answer is no more than 10−4, your solution will be accepted.
Sample Input
4
3 2 4 5
5
3 5 99 32 12
Sample Output
6.000000
52.833333
Source
2016 Multi-University Training Contest 3
1 2 3
1 2 3 用到了第3位
1 3 2 用到了第2位
2 1 3 用到了第1,3位
2 3 1 用到了第2位
3 1 2 用到了第1,3位
3 2 1 用到了第1位
总共有6种,第一位出现的3次,第二位出现了2次,第三位出现了3次。。
找个大点的排列直接打个表,观察每一位出现的频率,可观察得到第一位和最后一位出现频率为0.5,其他都是1/3;
There are two sequences h1∼hn and c1∼cn. h1∼hn is a permutation of 1∼n. particularly, h0=hn+1=0.
We define the expression [condition] is 1 when condition is True,is 0 when condition is False.
Define the function f(h)=∑ni=1ci[hi>hi−1 and hi>hi+1]
Bo have gotten the value of c1∼cn, and he wants to know the expected value of f(h).
Input
This problem has multi test cases(no more than 12).
For each test case, the first line contains a non-negative integer n(1≤n≤1000), second line contains n non-negative integer ci(0≤ci≤1000).
Output
For each test cases print a decimal - the expectation of f(h).
If the absolute error between your answer and the standard answer is no more than 10−4, your solution will be accepted.
Sample Input
4
3 2 4 5
5
3 5 99 32 12
Sample Output
6.000000
52.833333
Source
2016 Multi-University Training Contest 3
1 2 3
1 2 3 用到了第3位
1 3 2 用到了第2位
2 1 3 用到了第1,3位
2 3 1 用到了第2位
3 1 2 用到了第1,3位
3 2 1 用到了第1位
总共有6种,第一位出现的3次,第二位出现了2次,第三位出现了3次。。
找个大点的排列直接打个表,观察每一位出现的频率,可观察得到第一位和最后一位出现频率为0.5,其他都是1/3;
#include<cstdio> #include<cstring> #include<cmath> using namespace std; #define LL long long int main(){ int n; int a[1005]; while(scanf("%d",&n)!=EOF){ for(int i=1;i<=n;i++) scanf("%d",&a[i]); if(n==1){ printf("%d\n",a[1]); } else{ double ans=0; ans+=a[1]*0.5; ans+=a *0.5; for(int i=2;i<n;i++) ans+=a[i]*(1.0/3); printf("%f\n",ans); } } return 0; }
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