M - Youth Finale

https://codeforces.com/gym/104008/submission/179435878

Gym/104008/M/M.cpp

@@ -0,0 +1,78 @@
+#include <iostream>
+#include <deque>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 3e5 + 5;
+
+int n, m, p[N], c[N];
+long long ans;
+bool reversed;
+std::string s;
+std::deque<int> q;
+
+int lowbit(int x) {
+    return x & -x;
+}
+
+void add(int x, int y) {
+    for (; x <= n; x += lowbit(x)) c[x] += y;
+}
+
+int sum(int x) {
+    int res = 0;
+    for (; x; x -= lowbit(x)) res += c[x];
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> p[i];
+
+        q.emplace_back(p[i]);
+    }
+
+    for (int i = n; i; i--) {
+        ans += sum(p[i]);
+        add(p[i], 1);
+    }
+
+    cout << ans << endl;
+
+    cin >> s;
+
+    for (char c : s) {
+        if (c == 'S') {
+            int u;
+
+            if (reversed) {
+                u = q.back();
+                q.pop_back();
+                q.push_front(u);
+            } else {
+                u = q.front();
+                q.pop_front();
+                q.push_back(u);
+            }
+
+            ans += (n - 2 * u + 1);
+        } else {  // c == 'R'
+            reversed = !reversed;
+            ans = static_cast<long long>(n) * (n - 1) / 2 - ans;
+        }
+
+        cout << ans % 10;
+    }
+
+    cout << endl;
+
+    return 0;
+}