10533 - Digit Primes

[Eduard]

help please my program works fast and correct on my computer but gives WA. help pleas.[pascal]program acm10533;
var i,j,a,b,number,p,k,i1:longint;
c:array[0..1000000] of longint;
l:boolean;
procedure parz(n:longint;var h:boolean);
label 1;
var i:integer;
begin
h:=true;
for i:=2 to trunc(sqrt(n)) do
if n mod i=0 then begin h:=false;goto 1;end;
1:
end;
begin
read(number);
c[0]:=0;
for i:=1 to 1000000 do
begin
k:=0;
i1:=i;
parz(i,l);
if l=true then
begin
repeat
k:=k+(i mod 10);
i:=i div 10;
until i=0;
i:=i1;
parz(k,l);
if l=true then c[i]:=c[i-1]+1 else c[i]:=c[i-1];
end else c[i]:=c[i-1];
end;
for p:=1 to number do
begin
read(a,b);
writeln(c[b]-c[a]);
end;
end.
[/pascal]

[sohel]

Hi Eduard,
I am not an expert in interpreting PASCAL code, but here is some critical inputs.

What is your output for the following cases:

10
5 8
1 999999
11 25
3 3
5 6
6 7
1 100
9 10
200 300
12 13

[Eduard]

My answers are

1
30123
1
1
0
1
14
0
8
0

[osan]

INPUT
11
5 8
1 999999
11 25
3 3
5 6
6 7
1 100
9 10
200 300
12 13
1 10

OUTPUT
2
56
2
1
1
1
14
0
8
0
4

[pavelph]

Hi! I have TLE on this problem, but I don't know how I can make my program faster.
I have algo that:
1) get_primes_numbers (Eratosphean)
2) get_digit_primes_numbers
It makes

Code: Select all

d: array [1 .. 1000000] of boolean

and d[i]=true if i - digit prime. And this two procedures works <1 sec. !!!
It means that very slow work procedure that count how many 'true' values in array from t1 to t2. Help me please, how I can optimise this procedure:
[pascal] readln(n);
for i:=1 to n do begin
readln(n1, n2);
counter:=0;
if not odd(n1) then inc(n1);
while n1<=n2 do begin
if d[n1] then inc(counter);
inc(n1, 2);
end;
writeln(counter);
end;
[/pascal]

[UFP2161]

Have you ever considered a second lookup table that consists of the number of digit primes less than or equal to the index?

No point in repeating boolean checks for 1...999999, then 1...999998, then 1...999997, etc.

Just do it once, and extrapolate the answer given the range.

[pavelph]

Oh, yes, of course It's really very easy.
Thank you very much, now I have got AC on 10533 in 5 sec.

[soyoja]

First time, I tried to find amount of digit prime to use binary search...

( Using index of digit prime stored array )

But there are some problems...

( Binary search has some problem when an index value has no

digit prime, and so on... )

So I use 1,000,000 size integer array

and accumulate all digit prime, and range value to calculate

accumulated array.

P.S ) When I use Visual C++, I can only set 250,000 size integer

array. So I use gcc, and I can declare one million size int array.

[playerX]

i'm having wa... probably a small mistake, i'll look at it more attentively

[Kamanashish]

I can not understand what is the wrong with it.Have there any critical input?


//Cutted

[Rajib]

if(a[l]=='1')c++;

Do you think this portion will work correct...

13 is a prime number but not a digit prime. But in that protion you increase c by one (c++) if lower bound (l) is prime only. You must test whether (l) is a digit prime...

Test these:

Input:

3
3 5
13 13
11 13

Output:

2
0
1

Goodluck...
All the part of your code seem correct. Cut the code if you get AC.

[Kamanashish]

Thanks Rajib. At last i have got AC.

[jahangirk]

i m getting time limit exceed . plz help me i dont know y



[cpp]




#include<stdio.h>



bool checkprime(int num)
{
int flag=0;

if(num==2)
{
return true;
}
else
{
int count=2;
while(count<=(num/2)+1)
{
flag = 0;
if((num%count)==0)
{
flag=1;
break;
}
count=count+1;
}
if(flag!=1)
{
return true;
}
return false;
}


}




int main()
{
bool v;
int lim;
int i;

scanf("%d",&lim);

int upper,lower;

for(int k=0;k<lim;k++)
{
int total=0;

scanf("%d",&lower);
scanf("%d",&upper);




for(i=lower;i<upper;i++)
{



v=checkprime(i);

if(v==true)
{

int sum=0;

if(i>10)
{
int n=i;
int rem;


while(n>=10)
{
rem=n%10;
n=n/10;

sum=sum+rem;
}
sum=sum+n;

if(checkprime(sum))
{
total=total+1;
}


}

}
else
{
if(checkprime(i))
{
total=total+1;
}
}




}
printf("%d",total);
printf("\n");
}
return 0;
}


[/cpp]

[shamim]

Your prime testing method is highly inefficient. There are posts that has efficient method to test prime.

[Sanny]

Hi,
Besides the efficiency of ur prime testing function, there are other things u should look at.
As the number of test cases is 500000, u must use dynamic programming here.
And u better use the sieve method to generate all the primes.