#3872. 天天背单词

http://www.nfls.com.cn:20035/submission/587444

NFLSOJ/0/3872/3872.cpp

@@ -0,0 +1,160 @@
+#include <iostream>
+#include <fstream>
+#include <string>
+
+// using std::cin;
+// using std::cout;
+std::ifstream cin("prefix.in");
+std::ofstream cout("prefix.out");
+const char endl = '\n';
+
+const int N = 2.1e6 + 5;
+const int mod = 1e9 + 7;
+
+int n, k, fac[N], inv[N], fac_inv[N];
+
+class Trie {
+  private:
+    struct node {
+        int cnt;
+        bool is_end;
+        node *next[26];
+
+        node()
+            : cnt(0), is_end(false) {
+            std::fill_n(next, 26, nullptr);
+        }
+
+        ~node() {
+            for (int i = 0; i < 26; i++) {
+                if (next[i]) {
+                    delete next[i];
+                }
+            }
+        }
+    };
+
+    node *root;
+
+  public:
+    Trie()
+        : root(new node()) {}
+
+    ~Trie() {
+        delete root;
+    }
+
+    void insert(const std::string &s) {
+        node *cur = root;
+
+        for (auto c : s) {
+            if (cur->next[c - 'a'] == nullptr) {
+                cur->next[c - 'a'] = new node();
+            }
+
+            cur = cur->next[c - 'a'];
+            cur->cnt++;
+        }
+
+        cur->is_end = true;
+    }
+
+    int query(const std::string &s) {
+        node *cur = root;
+
+        for (auto c : s) {
+            if (cur->next[c - 'a'] == nullptr) {
+                return 0;
+            }
+
+            cur = cur->next[c - 'a'];
+        }
+
+        return cur->is_end ? cur->cnt : 0;
+    }
+
+    int rank(const std::string &s) {
+        node *cur = root;
+        int res = 0;
+
+        for (auto c : s) {
+            for (int i = 0; i < c - 'a'; i++) {
+                if (cur->next[i] != nullptr) {
+                    res += cur->next[i]->cnt;
+                }
+            }
+
+            if (cur->next[c - 'a'] == nullptr) {
+                return 0;
+            }
+
+            cur = cur->next[c - 'a'];
+        }
+
+        return res + 1;
+    }
+
+    void remove(const std::string &s) {
+        node *cur = root;
+
+        for (auto c : s) {
+            cur = cur->next[c - 'a'];
+            cur->cnt--;
+        }
+    }
+} trie;
+
+int A(int n, int m) {
+    return static_cast<long long>(fac[n]) * fac_inv[n - m] % mod;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k;
+
+    fac[0] = 1;
+    for (int i = 1; i < N; i++) {
+        fac[i] = static_cast<long long>(fac[i - 1]) * i % mod;
+    }
+
+    inv[0] = inv[1] = 1;
+    for (int i = 2; i < N; i++) {
+        inv[i] = static_cast<long long>(mod - (mod / i)) * inv[mod % i] % mod;
+    }
+
+    fac_inv[0] = fac_inv[1] = 1;
+    for (int i = 2; i < N; i++) {
+        fac_inv[i] = static_cast<long long>(fac_inv[i - 1]) * inv[i] % mod;
+    }
+
+    for (int i = 0; i < n; i++) {
+        std::string s;
+
+        cin >> s;
+
+        trie.insert(s);
+    }
+
+    int p = 1;
+    long long ans = 0;
+    std::string s, t;
+
+    cin >> s;
+
+    for (char c : s) {
+        t.push_back(c);
+
+        if (trie.query(t)) {
+            ans = (ans + static_cast<long long>(trie.rank(t) - 1) * A(n - p, k - p)) % mod;
+            trie.remove(t);
+            t.clear();
+            p++;
+        }
+    }
+
+    cout << (ans + 1) % mod << endl;
+
+    return 0;
+}