P3805 【模板】manacher 算法

https://www.luogu.com.cn/record/77959154

Luogu/P3805/P3805.cpp

@@ -0,0 +1,46 @@
+#include <iostream>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1.1e7 + 5;
+
+int p[N << 1], mid, r, ans;
+std::string s1, s2;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> s1;
+
+    // Init
+
+    s2.push_back('^');
+    for (const char &c : s1) {
+        s2.push_back('#');
+        s2.push_back(c);
+    }
+    s2 += "#$";
+
+    for (int i = 1; i < s2.size(); i++) {
+        p[i] = i < r ? std::min(p[mid * 2 - i], r - i) : 1;
+
+        while (s2[i - p[i]] == s2[i + p[i]]) p[i]++;
+
+        if (i + p[i] > r) {
+            r = i + p[i];
+            mid = i;
+        }
+    }
+
+    for (int i = 0; i < s2.size(); i++) {
+        ans = std::max(ans, p[i]);
+    }
+
+    cout << ans - 1 << endl;
+
+    return 0;
+}