题解 | #牛牛的排列数#
牛牛的排列数
http://www.nowcoder.com/practice/9ca1c236cdbf46da9e08e1f510808625
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
long n = scan.nextLong();
long m = scan.nextLong();
if(n<m) {
System.out.println(0);
return;
}
System.out.println(jc(n) / jc(n-m)); // 排列数的公式
}
public static long jc(long m) {
long tmp = 1;
for (int i=2;i<=m;i++) {
tmp *= i;
}
return tmp;
}
}
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