Gym 100917M Matrix, The

题目链接: http://codeforces.com/gym/100917/problem/M

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每次写$dp$都因为思路还不成熟就上了导致经常写出状态冗余的代码

这题看数据范围显然是状压$dp$

然后注意优雅地使用位运算来减少代码长度就好了

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
int ans[12], way[1 << 10];
long long f[11][1 << 10][1 << 10];
int n, a, b, q, cnt;
long long dfs(int r, int sta, int mask)
{
    long long &re = f[r][sta][mask];
    if(re != -1)
        return re;
    if(r == n)
        return re = (mask == (1 << n) - 1);
    re = 0;
    for(int i = 1; i <= cnt; ++i)
        if(!((~sta) & way[i] & mask))
            re += dfs(r + 1, way[i], way[i] | mask);
    return re;
}
bool dfs2(long long x, int r, int sta, int mask)
{
    if(r == n)
        return 1;
    for(int i = 1; i <= cnt; ++i)
        if(!((~sta) & way[i] & mask))
        {
            if(x > f[r + 1][way[i]][way[i] | mask])
                x -= f[r + 1][way[i]][way[i] | mask];
            else
            {
                ans[r + 1] = way[i];
                return dfs2(x, r + 1, way[i], way[i] | mask);
            }
        }
    return 0;
}
int calc1(int x)
{
    int re = 0;
    for(; x; x -= x & -x, ++re);
    return re;
}
void output(int x)
{
    for(int i = n - 1; i >= 0; --i)
        printf("%d", (x & (1 << i)) != 0);
    puts("");
}
int main()
{
    memset(f, -1, sizeof f);
    scanf("%d%d%d%d", &n, &a, &b, &q);
    for(int i = 1; i < (1 << n); ++i)
    {
        int tmp = calc1(i);
        if(tmp >= a && tmp <= b)
            way[++cnt] = i;
    }
    long long x;
    dfs(0, 0, 0);
    while(q--)
    {
        scanf("%lld", &x);
        if(dfs2(x, 0, 0, 0))
        {
            for(int i = 1; i <= n; ++i)
                 output(ans[i]);
        }
        else
            puts("No such matrix.");
        puts("");
    }
    return 0;
}