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