LightOj 1234 Harmonic Number
2016-03-17 10:41
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Harmonic Number
DescriptionIn mathematics, the nth harmonic number is the sum of the reciprocals of the first n natural numbers:
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
解题思路:
直接打表肯定会超内存,因此可以先将n分为50一组,来进行打表记录,暴力即可。AC代码:
#include <iostream>#include <cstdio>
using namespace std;
double a[2000005];
int main(){
double sum = 0;
for(int i = 1; i <= 1e8; i++){
sum += (1.0/i);
if(i%50 == 0)
a[i/50] = sum;
}
int T,t = 1;
scanf("%d",&T);
while(T--){
int n;
scanf("%d",&n);
int id = n/50;
sum = a[id];
for(int i = id*50+1; i <= n; i++){
sum += (1.0/i);
}
printf("Case %d: %.8lf\n",t++,sum);
}
return 0;
}
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