SGU 231 — Prime Sum
只说一点:如果一个素数p是两个素数a和b的加和,那么a和b一定有且仅有一个为2…正确性显然…
筛法还是蛮快的.
{ SGU 231; Prime Sum - sqybi’s code}//for my winstyprogram sgu231_sqybi; var n, i, j, s: longint; p: array[1..1000000]of boolean;
begin readln(n); fillchar(p, sizeof(p), true); for i:=2 to n do if p[i] then for j:=2 to n div i do p[i*j] := false; s := 0; for i:=2 to n-2 do if p[i] and […]