Create aho-corasick.cpp

ps/string/aho-corasick/aho-corasick.cpp

@@ -0,0 +1,63 @@
+struct Trie{
+    Trie *go[26]{};
+    Trie *fail{};
+    bool output;
+
+    Trie(){
+        fill(go, go + 26, nullptr); output = false;
+    }
+    ~Trie(){
+        for (auto & i : go) delete i;
+    }
+    void insert(const string& key, int idx = 0){
+        if (idx == key.size()){
+            output = true; return;
+        }
+        int nxt = key[idx] - 'a';
+        if (!go[nxt]) go[nxt] = new Trie();
+        go[nxt]->insert(key, idx + 1);
+    }
+};
+
+void fail_link(Trie* root){
+    queue<Trie*> Q; root->fail = root;
+    Q.push(root);
+    while (!Q.empty()){
+        auto cur = Q.front(); Q.pop();
+        for (int i = 0; i < 26; i++){
+            Trie* nxt = cur->go[i];
+            if (nxt == nullptr) continue;
+
+            if (cur == root) {
+                nxt->fail = root;
+            }
+            else{
+                Trie* dest = cur->fail;
+                while (dest != root && dest->go[i] == nullptr){
+                    dest = dest->fail;
+                }
+                if (dest->go[i]) dest = dest->go[i];
+                nxt->fail = dest;
+            }
+
+            if (nxt->fail->output) nxt->output = true;
+            Q.push(nxt);
+        }
+    }
+}
+
+bool find(string& str, Trie* root){
+    Trie* cur = root;
+    bool ans = false;
+    for (int i = 0; str[i]; i++){
+        int nxt = str[i] - 'a';
+        while (cur != root && cur->go[nxt] == nullptr){
+            cur = cur->fail;
+        }
+        if (cur->go[nxt]) cur = cur->go[nxt];
+        if (cur->output){
+            ans = true; break;
+        }
+    }
+    return ans;
+}