ZOJ - 2625 (大数)
Rearrange Them
N people stand in a line, and we numbered them 1,2...n, and now you are asked to rearrange them. The ith people is considred in the front of the (i+1)th, after the rearrange, everyone the people in front of whom can not be the same one as before. How many different strategies you can do the rearrange.
Input:
Each test case just contains one integer, the number of people you have to rearrange.
Output:
The number of strategies you have to rearrange them, with the condition above.
Sample Input:
3
4
Sample Output:
3
11
打表找规律,a[n]=(n-1)*a[n-1]+(n-2)*a[n-2]; n<1000;
import java.util.Scanner; import java.math.BigInteger; public class Main { public static void main(String[] args) { BigInteger a[];a=new BigInteger[10005]; a[0]=BigInteger.valueOf(0); a[1]=BigInteger.valueOf(0); a[2]=BigInteger.valueOf(1); a[3]=BigInteger.valueOf(3); a[4]=BigInteger.valueOf(11); for(int i=5;i<=1000;i++) { a[i]=a[i-1].multiply(BigInteger.valueOf(i-1)).add(a[i-2].multiply(BigInteger.valueOf(i-2))); } Scanner read=new Scanner(System.in); int x; while(read.hasNext()){ x=read.nextInt(); System.out.println(a[x]); } } }
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