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

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cmath>
 4 #include <algorithm>
 5 using namespace std;
 6 int ans[12], way[1 << 10];
 7 long long f[11][1 << 10][1 << 10];
 8 int n, a, b, q, cnt;
 9 long long dfs(int r, int sta, int mask)
10 {
11     long long &re = f[r][sta][mask];
12     if(re != -1)
13         return re;
14     if(r == n)
15         return re = (mask == (1 << n) - 1);
16     re = 0;
17     for(int i = 1; i <= cnt; ++i)
18         if(!((~sta) & way[i] & mask))
19             re += dfs(r + 1, way[i], way[i] | mask);
20     return re;
21 }
22 bool dfs2(long long x, int r, int sta, int mask)
23 {
24     if(r == n)
25         return 1;
26     for(int i = 1; i <= cnt; ++i)
27         if(!((~sta) & way[i] & mask))
28         {
29             if(x > f[r + 1][way[i]][way[i] | mask])
30                 x -= f[r + 1][way[i]][way[i] | mask];
31             else
32             {
33                 ans[r + 1] = way[i];
34                 return dfs2(x, r + 1, way[i], way[i] | mask);
35             }
36         }
37     return 0;
38 }
39 int calc1(int x)
40 {
41     int re = 0;
42     for(; x; x -= x & -x, ++re);
43     return re;
44 }
45 void output(int x)
46 {
47     for(int i = n - 1; i >= 0; --i)
48         printf("%d", (x & (1 << i)) != 0);
49     puts("");
50 }
51 int main()
52 {
53     memset(f, -1, sizeof f);
54     scanf("%d%d%d%d", &n, &a, &b, &q);
55     for(int i = 1; i < (1 << n); ++i)
56     {
57         int tmp = calc1(i);
58         if(tmp >= a && tmp <= b)
59             way[++cnt] = i;
60     }
61     long long x;
62     dfs(0, 0, 0);
63     while(q--)
64     {
65         scanf("%lld", &x);
66         if(dfs2(x, 0, 0, 0))
67         {
68             for(int i = 1; i <= n; ++i)
69                  output(ans[i]);
70         }
71         else
72             puts("No such matrix.");
73         puts("");
74     }
75     return 0;
76 }