'commit'

TangDou/LuoGuBook/P3405_2.cpp

@@ -0,0 +1,23 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+int n;
+string a, B;
+int ans; //极限值是20000*20000=400000000,是不会爆int的
+unordered_map<string, int> _map;
+
+int main() {
+    cin >> n;
+    for (int i = 1; i <= n; i++) {
+        cin >> a >> b;
+        //如果反过来掉过去都一样，就不用计算
+        string a1 = a.substr(0, 2), b1 = b.substr(0, 2);
+        if (a1 != b1) {
+            _map[a1 + b1]++;
+            ans += _map[b1 + a1];
+        }
+    }
+    //输出结果
+    cout << ans << endl;
+    return 0;
+}