USACO sec1.4 Arithmetic Progressions

预处理+暴力，4.8s险过；

注意长度为N的等差数列是指总共有N个数，所以公差上界为2*M*M/(N-1)；

/*
PROG : ariprog
LANG : C
*/
# include <stdio.h>
# include <stdlib.h>

# define MAXN (62505 * 2)

int N, M, ans;
char f[MAXN];
short p[MAXN], q[MAXN];

void pre(void)
{
    int i, j, x;
    for (i = 0; i <= 250; ++i)
    for (j = i; j <= 250; ++j)
    {
        x = i*i + j*j;
        f[x] = 1;
        if ((!q[x] && !p[x]) || (j-i <= q[x]-p[x]))
            q[x] = j, p[x] = i;
    }
}

void search(int a, int inc)
{
    int i, t;
    for (i = 0; i < N; ++i)
    {
        t = a + inc*i;
        if (!f[t] || p[t]>M || q[t]>M) return ;
    }
    ++ans;
    printf("%d %d\n", a, inc);      
}

int main()
{
    freopen("ariprog.in", "r", stdin);
    freopen("ariprog.out", "w", stdout);

    int i, inc, lim, up;
    
    ans = 0;
    pre();    
    scanf("%d%d", &N, &M); up = M*M, lim = up*2/(N-1);
    for (inc = 1; inc <= lim; ++inc)
    for (i = 0; i <= up; ++i)
    {
        if (i+inc*(N-1) <= 2*up) search(i, inc);
    }
    if (!ans) puts("NONE");
    
    fclose(stdin);
    fclose(stdout);
    
    return 0;
}