https://atcoder.jp/contests/abc110/tasks/abc110_d
#includeusingnamespacestd;#defineintlonglongintn,m;//intb[250005],a[250005],c[250005],d[250005];vectorv;sets;intans=1,cnt,M=1e9+7,c[100050][35]={1};signedmain(){cin>>n>>m;for(inti=1;i0)ans=ans*c[cnt+n