From dee98098429149764b0f3d499f69062b13371164 Mon Sep 17 00:00:00 2001
From: Kotecha Udit Hitendra <64374551+kirito-udit@users.noreply.github.com>
Date: Sat, 2 Oct 2021 20:09:49 +0530
Subject: [PATCH] Create Aho-Corasick Algorithm.cpp

---
 Algorithms/Aho-Corasick Algorithm.cpp | 53 +++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 Algorithms/Aho-Corasick Algorithm.cpp

diff --git a/Algorithms/Aho-Corasick Algorithm.cpp b/Algorithms/Aho-Corasick Algorithm.cpp
new file mode 100644
index 0000000..b9bee51
--- /dev/null
+++ b/Algorithms/Aho-Corasick Algorithm.cpp	
@@ -0,0 +1,53 @@
+const int K = 26;
+
+struct Vertex {
+    int next[K];
+    bool leaf = false;
+    int p = -1;
+    char pch;
+    int link = -1;
+    int go[K];
+
+    Vertex(int p=-1, char ch='$') : p(p), pch(ch) {
+        fill(begin(next), end(next), -1);
+        fill(begin(go), end(go), -1);
+    }
+};
+
+vector<Vertex> t(1);
+
+void add_string(string const& s) {
+    int v = 0;
+    for (char ch : s) {
+        int c = ch - 'a';
+        if (t[v].next[c] == -1) {
+            t[v].next[c] = t.size();
+            t.emplace_back(v, ch);
+        }
+        v = t[v].next[c];
+    }
+    t[v].leaf = true;
+}
+
+int go(int v, char ch);
+
+int get_link(int v) {
+    if (t[v].link == -1) {
+        if (v == 0 || t[v].p == 0)
+            t[v].link = 0;
+        else
+            t[v].link = go(get_link(t[v].p), t[v].pch);
+    }
+    return t[v].link;
+}
+
+int go(int v, char ch) {
+    int c = ch - 'a';
+    if (t[v].go[c] == -1) {
+        if (t[v].next[c] != -1)
+            t[v].go[c] = t[v].next[c];
+        else
+            t[v].go[c] = v == 0 ? 0 : go(get_link(v), ch);
+    }
+    return t[v].go[c];
+}