P3449 [POI2006]PAL-Palindromes

https://www.luogu.com.cn/record/84232432

Luogu/P3449/P3449.cpp

@@ -0,0 +1,46 @@
+#include <iostream>
+#include <string>
+#include <unordered_map>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e6 + 5;
+
+int n;
+long long ans;
+std::string s[N];
+std::unordered_map<std::string, int> map;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, _; i <= n; i++) {
+        cin >> _ >> s[i];
+
+        map[s[i]]++;
+    }
+
+    for (int i = 1; i <= n; i++) {
+        std::string str, str1(s[i]);
+        str.reserve(s[i].size());
+        str1.reserve(s[i].size() << 1);
+
+        for (char c : s[i]) {
+            str.push_back(c);
+            str1.push_back(c);
+
+            if (map.count(str) && str1 == str + s[i]) {
+                ans += static_cast<long long>(map[str]) * 2;
+            }
+        }
+    }
+
+    cout << ans - n << endl;
+
+    return 0;
+}