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[..] of longint;
    mindiv                              :array[..] 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+,sum*prime[d],ans+ans div (p+));
    dfs(d+,,sum*prime[d+],ans*);
end;

begin
    read(n);
    if n= then
    begin
        writeln();
        halt;
    end;
    for i:= to  do
    begin
        if mindiv[i]= then
        begin
            inc(prime[]);
            prime[prime[]]:=i;
            mindiv[i]:=i;
        end;
        for j:= to prime[] do
        begin
            if prime[j]*i> then break;
            mindiv[i*prime[j]]:=prime[j];
            if i mod prime[j]= then break;
        end;
    end;
    dfs(,,,);
    writeln(ansx);
end.