Long Update

Author: anubhavitis

1-Codeforces/Live contests/Round 673 Div 3/F

@@ -16,7 +16,7 @@
 #define rrep(i,b,c) for(i=b; i>=c; --i)
 
 #define PI 3.14159265
-#define M 998244353
+#define M (int)1000000007
 #define LINF LONG_MAX
 #define INF INT_MAX
 
@@ -29,27 +29,21 @@ void solve(void) {
 string s;
 cin >> n >> s;
 
-int dp[n + 1][3] = {};
+int dp[3] = {}; int len=1;
 
 for (int i = 1; i <= n; ++i) {
-dp[i][0] = dp[i - 1][0];
-dp[i][1] = 2 * dp[i - 1][1];
-dp[i][2] = 2 * dp[i - 1][2];
 
-if (s[i - 1] == 'a')	dp[i][0]++;
-else if (s[i - 1] == 'b')	dp[i][1] += dp[i][0];
-else if (s[i - 1] == 'c')	dp[i][2] += dp[i][1];
+if (s[i - 1] == 'a')	dp[0] = (dp[0]+len)%M;
+else if (s[i - 1] == 'b')	dp[1] = (dp[1] + dp[0])%M;
+else if (s[i - 1] == 'c')	dp[2] = (dp[2] + dp[1])%M;
 else {
-dp[i][2] += dp[i - 1][1];
-dp[i][1] += dp[i - 1][0];
-dp[i][0]++;
+dp[2] = (3 * dp[2] + dp[1])%M;
+dp[1] = (3 * dp[1] + dp[0])%M;
+dp[0] = (3 * dp[0] + len)%M;
+len= (3*len)%M;
 }
 }
-
-for (int i = 0; i <= n; ++i) {
-cerr << dp[i][0] << " " << dp[i][1] << " " << dp[i][2] << endl;
-}
-cout << dp[n][2] << endl;
+cout << dp[2] << endl;
 
 }