3157: 国王奇遇记 & 3516: 国王奇遇记加强版 - BZOJ

果然我数学不行啊，题解君： http://www.cnblogs.com/zhuohan123/p/3726933.html

 const
     h=;
 var
     fac,facinv,powm,s:array[..]of int64;
     n,m:int64;

 function mexp(a,b:int64):int64;
 begin
     if b= then exit();
     mexp:=sqr(mexp(a,b>>))mod h;
     if b and = then mexp:=mexp*a mod h;
 end;

 function C(n,r:int64):int64;
 begin
     exit((fac[n]*facinv[r] mod h)*facinv[n-r] mod h);
 end;

 procedure main;
 var
     i,j:longint;
 begin
     read(n,m);
     if m= then
     begin
       write((n*(n+)div )mod h);
       exit;
     end;
     fac[]:=;
     for i:= to m do
       fac[i]:=fac[i-]*i mod h;
     facinv[m]:=mexp(fac[m],h-);
     facinv[]:=;
     for i:=m- downto  do
       facinv[i]:=facinv[i+]*(i+)mod h;
     powm[]:=;
     for i:= to m do
       powm[i]:=-powm[i-];
     s[]:=((mexp(m,n+)-m+h)mod h)*mexp(m-,h-)mod h;
     for i:= to m do
       begin
         s[i]:=mexp(n,i)*mexp(m,n+)mod h;
         for j:= to i- do
           s[i]:=(s[i]+powm[i-j]*(C(i,j)*s[j]mod h)+h)mod h;
         s[i]:=s[i]*mexp(m-,h-)mod h;
       end;
     write(s[m]);
 end;

 begin
     main;
 end.