10948 - The primary problem

[Obaida]

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Accepted now. But it takes so much time could any one give me a better formula.  

[yeasin_acm_solver]

Accepted

[helloneo]

Try this input

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101

My output is..

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101:
NO WAY!

Hope this help

[DD]

I just wonder that how those people who got 0.00 for this problem? Even they build prime table before, they two sum problem still need O(N) time by implementing hash. Really curious about this.

[saiful_islam]

Code: Select all

#include<stdio.h>
#define MAX 1000000
#define MAXH MAX/2

char pr[MAX/16+10];
int a[78599];

void seive()
{
    int l=1090,i,j;
    for(i=3;i<l;i +=2)
    {

        if(!(pr[i>>4]&(1<<((i>>1)&0x7))))
        {
            for(j=i*i/2;j<=MAXH;j +=i)
            pr[j>>3] |=(1<<(j&0x7));
        }
    }
}
void isprime()
{
    register int i,p=1;
    a[0]=2;
   for(i=3;i<=99993;i++)
   {
        if(!(pr[i>>4]&(1<<((i>>1)&0x7))))
        {
            a[p]=i;
			p++;
        }
    i++;
   }
}
int find ( int target, int first, int last)
{
    int mid;
	if (first > last)
		return -1;

	 mid = (first + last) / 2;
		if (a[mid]==target)
			return mid;

	if (a[mid]<target)
			return find( target, mid+1, last);

	return find(target, first, mid-1);

}
int main()
{
    int i,j,k,l,n,m;
    seive();
    isprime();

    while(scanf("%d",&n)&&n)
    {
        printf("%d:\n",n);
        if(n%2)
        {
            m= n-2;
            if(find(m, 0, 78498)>=0)
            {
                printf("2+%d",a[find(m, 0, 78498)]);
            }
            else
            printf("NO WAY!");
        }
        else
        {
            for(i=0;i+1;i++)
            {
                m = n-a[i];
                if(find(m, 0, 78498)>=0)
                {
                    printf("%d+%d",a[i],a[find(m, 0, 78498)]);
                    break;
                }
            }
        }
        printf("\n");
    }
	return 0;
}

[brianfry713]

Missing a 9 on line 25.

[alexiago]

I solved this problem by creating an array and a SET with all primes up to 1 million. I looped thru the array getting the difference between the number N that we are looking for and the prime (i.e. N - primes), if we have that difference in the SET we found our sum and print it.

[brianfry713]

If you resubmit you'll get TLE. Read this thread.

[uDebug]

Nothing tricky, just some boundary cases:

Thanks for these great test cases.

[uDebug]

I solved this problem by creating an array and a SET with all primes up to 1 million. I looped thru the array getting the difference between the number N that we are looking for and the prime (i.e. N - primes), if we have that difference in the SET we found our sum and print it.

This problem's almost identical to 543 - Goldbach's Conjecture. If you're having issues, try that problem first and then give this one a shot.

[battirunner]

i have test for all kind of possible case but still getting WA. need some help with tricky test case
here is my code
#include<stdio.h>
#include<cstdio>
int p=0;
int prm[136]={2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769};
int prime[1000005];
void primecheck()
{
int f;
for(int i=2;i<=1000005;i++)
{
f=0;
for(int j=0;j<136;j++)
{
if(i%prm[j]==0&&i!=prm[j])
{
f=1;
break;
}
}

if(f==0)
{
prime[p]=i;
p++;
}

}

p=0;


}
int main()
{

int n,a=1,f=0,t,flag=0,u=0,l=0;
primecheck();
while(1)
{

scanf("%d",&n);

if(n==0)
break;
t=n;
a=1;
printf("%d:\n",n);

for(int s=0;s<80000;s++)
{
if(prime[s]>=n)
{
p=s;
break;
}
}
u=p-1;
l=0;

while((u-l)>=0)
{

if(prime[l]+prime==n)
{
printf("%d+%d\n",prime[l],prime);
f=1;
break;
}
if(prime[l]+prime>n)
u--;

if(prime[l]+prime<n)
l++;
}


if(f==0)
printf("NO WAY!\n");
f=0;

}

return 0;
}

[lighted]

Your prime checking is wrong for numbers greater than 769 * 769. You must add to your prm arrary all primes less than 1000 to check primality of numbers less than million.

Input

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982084
0

Acc Output

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982084:
17+982067

Your Output

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982084:
3+982081

982081 is not a prime. 982081 = 991 * 991.

Use code tags. Don't forget to remove your code after getting accepted.

[samir_h]

Code: Select all

Accepted now. But it takes so much time could any one give me a better formula.  

@Obaida: The trick is generating/detecting prime numbers.