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尤拉常數(調和級數求和) Harmonic Number

In mathematics, the nth harmonic number is the sum of the reciprocals of the first n natural numbers:

這裡寫圖片描述
這裡寫圖片描述
In this problem, you are given n, you have to find Hn.
Input

Input starts with an integer T (≤ 10000), denoting the number of test cases.

Each case starts with a line containing an integer n (1 ≤ n ≤ 108).

Output

For each case, print the case number and the nth harmonic number. Errors less than 10-8 will be ignored.

Sample Input

12

1

2

3

4

5

6

7

8

9

90000000

99999999

100000000

Sample Output

Case 1: 1

Case 2: 1.5

Case 3: 1.8333333333

Case 4: 2.0833333333

Case 5: 2.2833333333

Case 6: 2.450

Case 7: 2.5928571429

Case 8: 2.7178571429

Case 9: 2.8289682540

Case 10: 18.8925358988

Case 11: 18.9978964039

Case 12: 18.9978964139

公式。。。記住就行
尤拉常數y=0.57721566490153286060651209
ans=log(n)+y+1.0/(2*n)

#include <iostream>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <stdio.h>
using namespace std;
typedef long long ll;
const int INF=0x3f3f3f3f;
const int maxn=1e4
; double f[maxn+5]; int main() { int T; cin>>T; f[1]=1; for(int i=2;i<=maxn;i++) f[i]=f[i-1]+1.0/i; for(int cas=1;cas<=T;cas++) { int n; cin>>n; if(n<=maxn) printf("Case %d: %.10lf\n",cas,f[n]); else { double ans=log(n)+0.57721566490153286060651209+1.0/(2*n); printf("Case %d: %.10lf\n",cas,ans); } } return 0; }