#1694. 【2022.10.25 联考】先辈

https://sjzezoj.com/submission/62212

S2OJ/1694/1694.cpp

@@ -0,0 +1,69 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e5 + 5;
+const int mod = 114514;
+
+int n, sum[N][26], pre[26][26], suf[26][26], cnt[26];
+long long ans;
+std::string s;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> s;
+
+    n = s.size();
+    s = ' ' + s;
+
+    for (int i = 1; i <= n; i++) {
+        std::copy_n(sum[i - 1], 26, sum[i]);
+        sum[i][s[i] - 'a']++;
+    }
+
+    for (int i = n; i; i--) {
+        cnt[s[i] - 'a']++;
+        for (int j = 0; j < 26; j++) {
+            if (s[i] - 'a' == j) continue;
+
+            suf[s[i] - 'a'][j] = (suf[s[i] - 'a'][j] + cnt[j]) % mod;
+        }
+    }
+
+    std::fill_n(cnt, 26, 0);
+    for (int i = 1; i <= n; i++) {
+        cnt[s[i] - 'a']++;
+
+        for (int j = 0; j < 26; j++) {
+            if (cnt[j] < 2 || s[i] - 'a' == j) continue;
+
+            pre[s[i] - 'a'][j] = (pre[s[i] - 'a'][j] + (static_cast<long long>(cnt[j]) * (cnt[j] - 1) / 2) % mod) % mod;
+        }
+
+        for (int j = 0; j < 26; j++) {
+            if (s[i] - 'a' == j) continue;
+
+            suf[s[i] - 'a'][j] = (suf[s[i] - 'a'][j] - (sum[n][j] - sum[i - 1][j]) % mod + mod) % mod;
+        }
+
+        for (int j = 0; j < 26; j++) {
+            for (int k = 0; k < 26; k++) {
+                if (j == k || j == s[i] - 'a' || k == s[i] - 'a') continue;
+
+                ans += static_cast<long long>(pre[k][j]) * suf[j][k];
+            }
+        }
+
+        ans %= mod;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}