Add palindromic tree

content/strings/PalindromicTree.h

@@ -0,0 +1,31 @@
+/**
+ * Author: Unknown
+ * Date: 2024-11-05
+ * License: CC0
+ * Source: notebook el vasito
+ * Status: untested
+ */
+
+#pragma once
+
+struct PalindromicTree {
+	static const ll alpha = 26;
+	struct Node {
+		ll len, link = 0, cnt = 1;
+		array<ll, alpha> to{};
+	};
+	vector<Node> ns;
+	ll last;
+	PalindromicTree() : last(0) {ns.pb({-1}); ns.pb({0});}
+	void add(ll i, string &s) {
+		ll p = last, c = s[i] - 'a';
+		while (s[i - ns[p].len - 1] != s[i]) p = ns[p].link;
+		if (ns[p].to[c]) last = ns[p].to[c], ns[last].cnt++;
+		else {
+			ll q = ns[p].link;
+			while (s[i - ns[q].len - 1] != s[i]) q = ns[q].link;
+			last = ns[p].to[c] = SZ(ns);
+			ns.pb({ns[p].len + 2, max(1ll, ns[q].to[c]), 1});
+		}
+	}
+};