241. 楼兰图腾

https://www.acwing.com/problem/content/submission/code_detail/13302049/

AcWing/241/241.cpp

@@ -0,0 +1,52 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, y[N], l[N], r[N], c1[N], c2[N];
+long long ans1, ans2;
+
+inline int lowbit(int x) {
+    return x & -x;
+}
+
+void add(int *c, int x, int y) {
+    for (; x <= n; x += lowbit(x)) c[x] += y;
+}
+
+int sum(int *c, int x) {
+    int ans = 0;
+    for (; x; x -= lowbit(x)) ans += c[x];
+    return ans;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+    for (int i = 1; i <= n; i++) {
+        cin >> y[i];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        l[i] = sum(c1, y[i] - 1);
+        add(c1, y[i], 1);
+    }
+
+    for (int i = n; i; i--) {
+        r[i] = sum(c2, y[i] - 1);
+        add(c2, y[i], 1);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        ans1 += 1ll * (i - 1 - l[i]) * (n - i - r[i]);
+        ans2 += 1ll * l[i] * r[i];
+    }
+
+    cout << ans1 << ' ' << ans2 << endl;
+
+    return 0;
+}