The Guo Jie of the NUC

Problem description

Guo Jie wants you to help him find the value of F.
Enter a description

Example of multi-group test sample.

A positive n (4<=n<=1e9) output description for each set of samples that is greater than 3

Each set of test sample output one row. (Results reserved 12 decimal places) sample input

4

Sample output

0.250000000000

SOURCE 12th session of the North University program design contest Tips

Hehe, secretly tell you, really white again in test Guo Jie Math ~

Ideas:

If the problem is calculated as equal to 4 and not equal to 4, then it will time out. So the main problem is to find 6/(n (n-1) * (n-2)) this law.

Timeout code:

#include <stdio.h>
#include <stdlib.h>/

* Run this program using the console Pauser or add your own GE TCH, System ("pause") or input loop *

/int main () {
	double n, sum = 1;
	int i;
	while (scanf ("%lf", &n)!=eof) {
		double A = n;
		if (n = = 4) {
			sum = 1.0 * 1.0/4;
			printf ("%.12f\n", sum);
		} else if (n>4) {for
			(i=1;i<n-3;i++) {
				sum *= i/a;
				a--;
			}
			printf ("%.12f\n", sum);
		
		}
		
	}
	return 0;
}

Correct code:

#include <stdio.h>
#include <stdlib.h>/

* Run this program using the console Pauser or add your own Getch, System ("pause") or input loop *

/int main () {
	double n, sum = 0;
	while (scanf ("%lf", &n)!=eof) {
		sum = 6/(n (n-1) * (n-2));
		printf ("%.12f\n", sum);
		
	}
	return 0;
}