PAT 1007 素数对猜想

传送门
筛法素数打表->枚举
╮(╯-╰)╭

#include <stdio.h>
#include <math.h>
#include <string.h>
#define INF 1<<20
int main()
{
    long long i,j;
    char isPrime[INF];
    memset(isPrime,1,sizeof(isPrime));
    isPrime[0] = isPrime[1] = 0;
    for(i=2; i<=INF; i++)
        for(j=i*2; j<=INF; j+=i)
            isPrime[j] = 0;
    int k,N,ans = 0;
    scanf("%d",&N);
    for(k=3; k<=N; k+=2)
        if(isPrime[k])
            if(isPrime[k]-isPrime[k-2]==0)
                ans++;
    printf("%d",ans);
    return 0;
}