素数距离问题

http://acm.nyist.net/JudgeOnline/problem.php?pid=24

 

方法一

#include<stdio.h>

int isPrime(int num)
{
	if(num==1)return 0;
	for(int i=2;i*i<=num;i++)
		if(num%i==0)
			return 0;
	return 1;
}

int main()
{
	int n,num,numUp,numDown,deltUp,deltDown;
	scanf("%d",&n);
	while(n--)
	{
		scanf("%d",&num);
		if(isPrime(num))//本身是素数，后面就不用了 
		  printf("%d 0\n",num);
		else
		{
    		numUp=numDown=num;
    		while(!isPrime(numUp))
    		{
    			numUp+=1;
    		}
    		while(!isPrime(numDown)&&numDown>0)//边界条件，否则不能通过 
    		{
    			numDown-=1;
    		}
    		deltUp = numUp-num;
    		deltDown = num-numDown;
    		
    		if(numDown==0)//特殊情况：左边没有找到 
    		  printf("%d %d\n",numUp,deltUp);
    		else if(deltUp>=deltDown)//输出距离小的, 相等则左 
    			printf("%d %d\n",numDown,deltDown);
    		else
    			printf("%d %d\n",numUp,deltUp);
        }

	}
	
	return 0;
}
                

 

 

方法二

 

#include<stdio.h>
#include<string.h>
#define max 1000000
int a[max+100];

int main()
{	

	int i,j;
	memset(a,0,sizeof(a));
	a[1]=1;
	for(i=2;i<=max+10;++i)//这个地方把我坑了，max+10 
	{
		for(j=2*i;j<=max+10;j+=i)
		{
			a[j]=1;
		}
	} 
	int t;
	scanf("%d",&t);
	int m;
	while(t--)
	{		
		int temp1,temp2;
		scanf("%d",&m);
		temp1=temp2=m;
		if(a[m]==0)
		printf("%d 0\n",m);		
		else
		{		
			int left,right;
			while(a[temp1]==1)
			{			
				++temp1;				
			}
			while(a[temp2]==1&&temp2>0)
			{			
				--temp2;						
			}
			left=m-temp2;
			right=temp1-m;
			if(temp2==0)			
				printf("%d %d\n",temp1,right);			
			else if(left<=right)
			printf("%d %d\n",temp2,left);
			else
			printf("%d %d\n",temp1,right);			
		}
	}
	return 0;
}