【dp】Arrange the Schedule

 1 /***Good Luck***/
 2 #define _CRT_SECURE_NO_WARNINGS
 3 #include <iostream>
 4 #include <cstdio>
 5 #include <cstdlib>
 6 #include <cstring>
 7 #include <string>
 8 #include <algorithm>
 9 #include <stack>
10 #include <map>
11 #include <queue>
12 #include <vector>
13 #include <set>
14 #include <functional>
15 #include <cmath>
16 #include <numeric>
17 
18 #define Zero(a) memset(a, 0, sizeof(a))
19 #define Neg(a)  memset(a, -1, sizeof(a))
20 #define All(a) a.begin(), a.end()
21 #define PB push_back
22 #define inf 0x3f3f3f3f
23 #define inf2 0x7fffffffffffffff
24 #define ll long long
25 using namespace std;
26 //#pragma comment(linker, "/STACK:102400000,102400000")
27 void get_val(int &a) {
28     int value = 0, s = 1;
29     char c;
30     while ((c = getchar()) == ‘ ‘ || c == ‘\n‘);
31     if (c == ‘-‘) s = -s; else value = c - 48;
32     while ((c = getchar()) >= ‘0‘ && c <= ‘9‘)
33         value = value * 10 + c - 48;
34     a = s * value;
35 }
36 const int maxn = 14;
37 pair<char, int> pr[maxn];
38 int n, m;
39 ll mod = 1000000007;
40 inline ll modxp(ll a, ll b, ll mod) {
41     ll ret = 1;
42     ll tmp = a;
43 
44     while (b) {
45         if (b & 1) ret = ret* tmp %mod;
46         tmp = tmp * tmp % mod;
47         b >>= 1;
48     }
49     return ret;
50 }
51 
52 bool cmp(pair<char, int> a, pair<char, int> b) {
53     return a.second < b.second;
54 }
55 int main() {
56     //freopen("data.out", "w", stdout);
57     //freopen("data.in", "r", stdin);
58     //cin.sync_with_stdio(false);
59     while (cin >> n >> m) {
60         ll ans = 1;
61         if (m == 0) {
62             cout << (4 * modxp(3, n - 1, mod)) % mod << endl;
63             continue;
64         }
65         for (int i = 1; i <= m; ++i) {
66             cin >> pr[i].second >> pr[i].first;
67         }
68         sort(pr + 1, pr + m + 1, cmp);
69         ans *= modxp(3, pr[1].second - 1, mod);
70         ans *= modxp(3, n - pr[m].second, mod);
71         ans %= mod;
72         ll t;
73         bool flag = false;
74         for (int i = 2; i <= m; ++i) {
75             if (pr[i].first == pr[i - 1].first && pr[i].second - pr[i - 1].second == 1) {
76                 cout << 0 << endl;
77                 flag = true;
78                 break;
79             }
80             if (pr[i].second - pr[i - 1].second == 1) continue;
81 
82             else {
83                 t = pr[i].second - pr[i - 1].second;
84                 if (pr[i].first == pr[i - 1].first) {
85                     ans *= ((3 * ((t & 1) ? -1 : 1) + modxp(3, t, mod))  * 250000002) % mod ;
86                     ans %= mod;
87                 }
88                 else {
89                     ans *= ((((t & 1) ? 1 : -1) + modxp(3, t, mod)) * 250000002) % mod;
90                     ans %= mod;
91                 }
92             }
93         }
94         if (!flag) 
95         cout << ans << endl;
96     }
97     return 0;
98 }