#1745. 【2022.11.8 NOIP 模拟赛】石蒜反冲（lycoris）

https://sjzezoj.com/submission/63909

S2OJ/1745/1745.cpp

@@ -0,0 +1,68 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 10005,
+          K = 2005;
+const int mod = 993244353;
+
+const std::string s1 = "sakana";
+const std::string s2 = "chinanago";
+
+int n, k, _f[N][K], *f[N];
+std::string s;
+
+bool check(const std::string &pat, const std::string &str) {
+    if (pat.size() != str.size()) return false;
+
+    for (int i = 0; i < pat.size(); i++) {
+        if (pat[i] != '?' && pat[i] != str[i]) return false;
+    }
+
+    return true;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> s;
+
+    k = n / std::max(s1.size(), s2.size());
+    s = ' ' + s;
+
+    for (int i = 0; i <= n; i++) {
+        f[i] = _f[i] + k + 1;
+    }
+
+    f[0][0] = 1;
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = -k; j <= k; j++) {
+            if (s[i] == '?') f[i][j] = (f[i][j] + static_cast<long long>(f[i - 1][j]) * 26 % mod) % mod;
+            else f[i][j] = f[i - 1][j];
+        }
+
+        if (i >= s1.size() && check(s.substr(i - s1.size() + 1, s1.size()), s1)) {
+            for (int j = -k; j <= k; j++) {
+                f[i][j] = ((f[i][j] - f[i - s1.size()][j]) % mod + mod) % mod;
+                f[i][j + 1] = (f[i][j + 1] + f[i - s1.size()][j]) % mod;
+            }
+        }
+
+        if (i >= s2.size() && check(s.substr(i - s2.size() + 1, s2.size()), s2)) {
+            for (int j = -k; j <= k; j++) {
+                f[i][j] = ((f[i][j] - f[i - s2.size()][j]) % mod + mod) % mod;
+                f[i][j - 1] = (f[i][j - 1] + f[i - s2.size()][j]) % mod;
+            }
+        }
+    }
+
+    cout << f[n][0] << endl;
+
+    return 0;
+}