USACO sec2.1 Hamming Codes

直接枚举就行了，不带回溯的搜索。

/*
PROG : hamming
LANG : C++
*/
# include <stdio.h>

# define id(x) ((x)>>3)
# define of(x) ((x)&0x7)
# define get(x) ((h[id(x)]>>of(x))&0x1)
# define set(x) (h[id(x)] |= (0x1<<of(x)))

int n, b, d;
char h[(1<<5) + 1];
int sol[70];
/*************************************************/
int dis(int x, int y)
{
    int s = x ^ y, r = 0;
    while (s)
    {
        ++r;
        s &= s-1;
    }
    return r;
}

void search(int cur, int cnt)
{
    int i, j;
    if (cnt > n) return ;
    for (i = cur+1; i < (1<<b); ++i) if (!get(i))
    {
        for (j = 1; j <= cnt; ++j)
            if (dis(sol[j], i) < d) break;
        set(i);
        if (j > cnt) {sol[cnt+1] = i; search(i, cnt+1);}
    }
}
/*************************************************/
void solve(void)
{
    int i;
    scanf("%d%d%d", &n, &b, &d);
    sol[1] = 0, set(0);
    search(0, 1);
    for (i = 1; i <= n; ++i)
    {
        if (i%10 != 1) putchar(' ');
        printf("%d", sol[i]);
        if (i<n && i%10 == 0) putchar('\n');
    }
    putchar('\n');
}

int main()
{
    freopen("hamming.in", "r", stdin);
    freopen("hamming.out", "w", stdout);
    
    solve();
    
    fclose(stdin);
    fclose(stdout);
    
    return 0;
}