bzoj1053 搜索

2013-11-16 17:43

原题传送门http://www.lydsy.com/JudgeOnline/problem.php?id=1053

因为使pi(prime[i])<20亿的i不会太大，大概二十几，所以直接搜就行了

//By BLADEVIL

var

    n                                   :int64;

    prime                               :array[0..100] of longint;

    mindiv                              :array[0..10000] of longint;

    i, j                                :longint;

    ansnum, ansx                        :int64;

     

procedure dfs(d,p,sum,ans:int64);

var

    i                                   :longint;

     

begin

    if sum>n then exit;

    if (ans>ansnum) or (ans=ansnum) and (sum<ansx) then

    begin

        ansx:=sum;  

        ansnum:=ans;

    end;

    if(sum*prime[d]>n) then exit;

     

    dfs(d,p+1,sum*prime[d],ans+ans div (p+1));

    dfs(d+1,1,sum*prime[d+1],ans*2);

end;

     

begin

    read(n);

    if n=1 then

    begin

        writeln(1);

        halt;

    end;

    for i:=2 to 40 do

    begin

        if mindiv[i]=0 then

        begin

            inc(prime[0]);

            prime[prime[0]]:=i;

            mindiv[i]:=i;

        end;

        for j:=1 to prime[0] do

        begin

            if prime[j]*i>40 then break;

            mindiv[i*prime[j]]:=prime[j];

            if i mod prime[j]=0 then break;

        end;

    end;

    dfs(1,1,2,2);

    writeln(ansx);

end.