'commit'

TangDou/AcWing/BIT/241_BIT.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+typedef long long LL;
+const int N = 200010;
+
+int n, a[N];         // n个元素，a[i]代表原始值
+LL big[N], small[N]; // big[i]:比a[i]大的元素个数，small[i]:比a[i]小的元素个数
+LL res1, res2;       // V的个数，∧的个数
+
+// 树状数组模板
+typedef long long LL;
+#define lowbit(x) (x & -x)
+int c[N];
+void add(int x, int d) {
+    for (int i = x; i < N; i += lowbit(i)) c[i] += d;
+}
+LL sum(int x) {
+    LL res = 0;
+    for (int i = x; i; i -= lowbit(i)) res += c[i];
+    return res;
+}
+
+// 桶计数+前缀和
+int main() {
+    scanf("%d", &n);
+    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
+
+    for (int i = 1; i <= n; i++) { // 枚举每个点，由左到右一个个下场
+        int x = a[i];
+        small[i] = sum(x - 1);        // 在我前面出场，并且，值比我小, 用于方便统计铁锹(∧)
+        big[i] = sum(n) - sum(x - 1); // 在我前面出场，并且，值比我大, 用于方便统计尖刀(V)
+        add(x, 1);                    // 以值为桶的标识，记录此桶中数量+1
+    }
+
+    memset(c, 0, sizeof c);
+
+    for (int i = n; i; i--) {
+        int x = a[i];
+        res1 += small[i] * sum(x - 1);
+        res2 += big[i] * (sum(n) - sum(x - 1));
+        add(x, 1);
+    }
+    printf("%lld %lld\n", res2, res1);
+    return 0;
+}