
ZOJ Problem Set  2284
Let { A1,A2,...,An } be a permutation of the set{ 1,2,..., n}. The inversion number of the permutation is the number of integer pairs (i,j) that satisfy 1<=i<j<=n and Ai>Aj.
The input consists of several test cases. Each test case contains two integers n(0<n<=20) and k(0<=k<=200), which are mentioned above. Input is terminated by n=m=0, which should not be proceeded.
For each case of input output the number of npermutations that has an inversion number of k in one line.
2 0
1
Author: GUAN, Yao Source: ZOJ Monthly, January 2005 