做sprime这道题，用dfs做的，手测没问题，提交后……
Run 3: Execution error: Your program had this runtime error: Bad
syscall #32000175 (RT_SIGPROCMASK) [email kolstad if you think
this is wrong]. The program ran for 0.000 CPU seconds before the
error. It used 276 KB of memory.
------ Data for Run 3 [length=2 bytes] ------
6
----------------------------


这是代码：
const number:array[1..4]of integer=(1,3,7,9);number2:array[1..4]of integer=(2,3,5,7);var n:integer;now:longint;function prime(x:longint):boolean;var i:longint;begin for i:=2 to trunc(sqrt(x)) do if x mod i=0 then exit(false); exit(true);end;procedure dfs(k:integer);var i:integer;mid:integer;begin if k=n+1 then begin writeln(now);exit;end; for i:=1 to 4 do if k=1 then begin now:=number2[i]; dfs(k+1); now:=0; end else begin mid:=now; now:=now*10+number[i]; if prime(now)then dfs(k+1); now:=mid; end;end;begin assign(input,'sprime.in');reset(input);assign(output,'sprime.out');rewrite(output); readln(n); now:=0; dfs(1); close(input);close(output);end.

检查一下数组越界