XDOJ-1002最喜欢的数字

大神代码赏析：

#include<stdio.h>
#define N    100000
int main()
{
    int e[N+1] = {0}, p[N], pn = 0, an, m, i, j, t;

    for(i = 2; i <= N; e[i++] = 1);

    for(i = 2; i <= N; i++)
    if(e[i]) for(p[pn++] = i, j = i + i; j <= N; j += i) e[j] = 0;

    for(an = pn, i = 0; an < N - 1; i++)
    {
        if((t = p[i] + 1) <= N && !e[t]) e[p[an++] = t] = e[p[i]] + 1;

        for(j = 0, m = N / p[i]; j < pn && p[j] <= m; j++)
        if(!e[t = p[i] * p[j]]) e[p[an++] = t] = e[p[i]] + 1;
    }

    for(i = 3; i <= N; i++) e[i] += e[i - 1];

    while(scanf("%d%d", &i, &j) != EOF) printf("%d\n", e[j] - e[i - 1]);

    return 0;
}