CodeForcesGym 100212E Long Dominoes

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 typedef long long LL;
 4 const int maxn = 1<<18;
 5 LL dp[2][maxn];
 6 vector<int>g[maxn];
 7 bool tab[10][10];
 8 int stx[maxn],tot;
 9 void dfs(int row,int st,int n) {
10     if(row == n) {
11         int tst = 0;
12         for(int i = n-1; i >= 0; --i) {
13             tst <<= 2;
14             tst |= tab[i][1]|(tab[i][2]<<1);
15         }
16         g[tst].push_back(st);
17         stx[tot++] = tst;
18         stx[tot++] = st;
19         return;
20     }
21     if(!tab[row][0]) {
22         if(!tab[row][1] && !tab[row][2]) {
23             tab[row][0] = tab[row][1] = tab[row][2] = true;
24             dfs(row + 1,st,n);
25             tab[row][0] = tab[row][1] = tab[row][2] = false;
26         }
27         if(row + 3 > n || tab[row + 1][0] || tab[row + 2][0]) return;
28         tab[row + 2][0] = tab[row + 1][0] = tab[row][0] = true;
29         dfs(row + 3,st,n);
30         tab[row + 2][0] = tab[row + 1][0] = tab[row][0] = false;
31     } else dfs(row + 1,st,n);
32 }
33 void init(int st,int n) {
34     memset(tab,false,sizeof tab);
35     for(int i = 0,xst = st; i < n; ++i,xst >>= 2) {
36         int row = xst&3;
37         tab[i][0] = row&1;
38         tab[i][1] = (row>>1)&1;
39         if(row == 2) return;
40     }
41     dfs(0,st,n);
42 }
43 int main() {
44     freopen("dominoes.in","r",stdin);
45     freopen("dominoes.out","w",stdout);
46     int m,n;
47     scanf("%d%d",&m,&n);
48     for(int i = 0; i < (1<<(m + m)); ++i) init(i,m);
49     sort(stx,stx + tot);
50     tot = unique(stx,stx + tot) - stx;
51     int cur = dp[0][0] = 1;
52     for(int i = 1; i <= n; ++i) {
53         for(int j = 0; j < tot; ++j) {
54             for(int k = g[stx[j]].size()-1; k >= 0; --k)
55                 dp[cur][stx[j]] += dp[cur^1][g[stx[j]][k]];
56         }
57         cur ^= 1;
58         memset(dp[cur],0,sizeof dp[cur]);
59     }
60     printf("%I64d\n",dp[cur^1][0]);
61     return 0;
62 }