【BZOJ4517】排列计数（排列组合）

题意：1-n的一个序列，其中有m个a[i]=i，求方案数

n,m<=1000000

题意：显然ANS=c(n,m)*d[n-m]

d[i]为错排方案数=d[i-1]*n+(-1)^n

 const mo=;
 var fac,exf,d:array[..]of int64;
     cas,i,n,m:longint;

 function c(x,y:longint):int64;
 begin
  exit(fac[x]*exf[y] mod mo*exf[x-y] mod mo);
 end;

 begin
  assign(input,'bzoj4517.in'); reset(input);
  assign(output,'bzoj4517.out'); rewrite(output);
  d[]:=;
  for i:= to  do
  begin
   d[i]:=d[i-]*i;
   if i and = then inc(d[i])
    else dec(d[i]);
   d[i]:=d[i] mod mo;
  end;
  fac[]:=; exf[]:=; exf[]:=;
  for i:= to  do fac[i]:=fac[i-]*i mod mo;
  for i:= to  do exf[i]:=exf[mo mod i]*(mo-mo div i) mod mo;
  for i:= to  do exf[i]:=exf[i-]*exf[i] mod mo;
  readln(cas); d[]:=;
  for i:= to cas do
  begin
   readln(n,m);
   writeln(c(n,m)*d[n-m] mod mo);
  end;
  close(input);
  close(output);
 end.