P7868 [COCI2015-2016#2] VUDU

https://www.luogu.com.cn/record/76401826

Luogu/P7868/P7868.cpp

@@ -0,0 +1,56 @@
+#include <algorithm>
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+
+int n, p, a[N];
+long long b[N], ans;
+
+void solve(int l, int r) {
+    if (l == r) {
+        if (a[l] >= p) ans++;
+        return;
+    }
+
+    int mid = l + r >> 1;
+
+    solve(l, mid);
+    solve(mid + 1, r);
+
+    b[mid] = a[mid] - p;
+    for (int i = mid - 1; i >= l; i--) b[i] = b[i + 1] + a[i] - p;
+    std::sort(b + l, b + mid + 1);
+
+    b[mid + 1] = a[mid + 1] - p;
+    for (int i = mid + 2; i <= r; i++) b[i] = b[i - 1] + a[i] - p;
+    std::sort(b + mid + 1, b + r + 1);
+
+    int i = l, j = r;
+    while (i <= mid) {
+        while (j > mid && b[i] + b[j] >= 0) j--;
+        ans += r - j;
+        i++;
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    cin >> p;
+
+    solve(1, n);
+
+    cout << ans << endl;
+
+    return 0;
+}