From aa9704c34629d95c095a0d6d59b552ce59ea600d Mon Sep 17 00:00:00 2001
From: hitonanode <32937551+hitonanode@users.noreply.github.com>
Date: Sat, 29 Nov 2025 14:52:59 +0900
Subject: [PATCH 1/2] fix manacher

---
 string/manacher.hpp                    |  7 +++++--
 string/manacher.md                     |  5 +++++
 string/test/manacher.yuki3392.test.cpp | 22 ++++++++++++++++++++++
 3 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 string/test/manacher.yuki3392.test.cpp

diff --git a/string/manacher.hpp b/string/manacher.hpp
index 62d811d7..7e38e1f2 100644
--- a/string/manacher.hpp
+++ b/string/manacher.hpp
@@ -3,7 +3,6 @@
 #include <utility>
 #include <vector>
 
-// CUT begin
 // Manacher's Algorithm: radius of palindromes
 // Input: std::string or std::vector<T> of length N
 // Output: std::vector<int> of size N
@@ -30,8 +29,13 @@ std::vector<int> manacher(const std::string &S) {
     return manacher(v);
 }
 
+// Find maximal palindrome length for each center
+// input: array of length N
+// output: array of length N * 2 - 1
 template <typename T>
 std::vector<std::pair<int, int>> enumerate_palindromes(const std::vector<T> &vec) {
+    if (vec.empty()) return {};
+
     std::vector<T> v;
     const int N = vec.size();
     for (int i = 0; i < N - 1; i++) {
@@ -52,7 +56,6 @@ std::vector<std::pair<int, int>> enumerate_palindromes(const std::vector<T> &vec
     }
     return ret;
 }
-
 std::vector<std::pair<int, int>> enumerate_palindromes(const std::string &S) {
     std::vector<char> v(S.size());
     for (int i = 0; i < int(S.size()); i++) v[i] = S[i];
diff --git a/string/manacher.md b/string/manacher.md
index 2e15edac..827ee13f 100644
--- a/string/manacher.md
+++ b/string/manacher.md
@@ -16,6 +16,11 @@ for (auto [l, r] : palindromes) {
 }
 ```
 
+## 問題例
+
+- [Enumerate Palindromes](https://judge.yosupo.jp/problem/enumerate_palindromes)
+- [No.3392 Count 23578 Sequence - yukicoder](https://yukicoder.me/problems/no/3392)
+
 ## 文献
 
 - [1] G. Manacher, "A new linear-time "on-line" algorithm for finding the smallest initial palindrome of a string", Journal of the ACM, 22 (3), 346-351, 1975.
diff --git a/string/test/manacher.yuki3392.test.cpp b/string/test/manacher.yuki3392.test.cpp
new file mode 100644
index 00000000..21fe81e3
--- /dev/null
+++ b/string/test/manacher.yuki3392.test.cpp
@@ -0,0 +1,22 @@
+#define PROBLEM "https://yukicoder.me/problems/no/3392"
+#include "../manacher.hpp"
+
+#include <iostream>
+using namespace std;
+
+int main() {
+    cin.tie(nullptr), ios::sync_with_stdio(false);
+
+    int N;
+    cin >> N;
+    vector<int> A(N);
+    for (auto &a : A) cin >> a;
+
+    vector<int> D(N - 1);
+    for (int i = 0; i < N - 1; ++i) D.at(i) = A.at(i + 1) - A.at(i);
+
+    long long ret = N;
+    for (auto [l, r] : enumerate_palindromes(D)) ret += (r - l + 1) / 2;
+
+    cout << ret << '\n';
+}

From 455f8a406f087e96bb5107ef9b3b2088d83451a5 Mon Sep 17 00:00:00 2001
From: hitonanode <32937551+hitonanode@users.noreply.github.com>
Date: Mon, 1 Dec 2025 22:55:59 +0900
Subject: [PATCH 2/2] fix existing tests of manacher

---
 graph/test/shortest_path_dial.yuki1695.test.cpp | 3 ++-
 graph/test/zero_one_bfs.yuki1695.test.cpp       | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/graph/test/shortest_path_dial.yuki1695.test.cpp b/graph/test/shortest_path_dial.yuki1695.test.cpp
index 3947b758..5f7ebc74 100644
--- a/graph/test/shortest_path_dial.yuki1695.test.cpp
+++ b/graph/test/shortest_path_dial.yuki1695.test.cpp
@@ -14,6 +14,7 @@ int solve(const string &S, const string &T) {
     if (!nmatch) return INF;
     if (T.size() % 2) return INF;
     auto trev = T;
+    reverse(trev.begin(), trev.end());
     if (trev != T) return INF;
     shortest_path<int> graph(T.size() + 1);
     for (int i = 0; i < int(T.size()); ++i) graph.add_edge(i, i + 1, 0);
@@ -23,7 +24,7 @@ int solve(const string &S, const string &T) {
         if ((l + r) % 2 == 0) graph.add_edge(r, (l + r) / 2, 1);
     }
     graph.dial(T.size(), nmatch);
-    return graph.dist[nmatch];
+    return std::max(1, graph.dist[nmatch]);
 }
 
 int main() {
diff --git a/graph/test/zero_one_bfs.yuki1695.test.cpp b/graph/test/zero_one_bfs.yuki1695.test.cpp
index 68fa6573..6a9314f7 100644
--- a/graph/test/zero_one_bfs.yuki1695.test.cpp
+++ b/graph/test/zero_one_bfs.yuki1695.test.cpp
@@ -14,6 +14,7 @@ int solve(const string &S, const string &T) {
     if (!nmatch) return INF;
     if (T.size() % 2) return INF;
     auto trev = T;
+    reverse(trev.begin(), trev.end());
     if (trev != T) return INF;
     shortest_path<int> graph(T.size() + 1);
     for (int i = 0; i < int(T.size()); ++i) graph.add_edge(i, i + 1, 0);
@@ -23,7 +24,7 @@ int solve(const string &S, const string &T) {
         if ((l + r) % 2 == 0) graph.add_edge(r, (l + r) / 2, 1);
     }
     graph.zero_one_bfs(T.size(), nmatch);
-    return graph.dist[nmatch];
+    return std::max(1, graph.dist[nmatch]);
 }
 
 int main() {