P3605 [USACO17JAN]Promotion Counting P

https://www.luogu.com.cn/record/86666473

Luogu/P3605/P3605.cpp

@@ -0,0 +1,72 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, p[N], c[N], ans[N];
+std::vector<int> nums, g[N];
+
+inline int lowbit(int x) {
+    return x & -x;
+}
+
+inline void add(int x, int y) {
+    for (; x <= n; x += lowbit(x)) c[x] += y;
+}
+
+inline int sum(int x) {
+    int res = 0;
+    for (; x; x -= lowbit(x)) res += c[x];
+    return res;
+}
+
+void dfs(int u) {
+    ans[u] -= sum(n) - sum(p[u]);
+
+    for (int v : g[u]) {
+        dfs(v);
+    }
+
+    ans[u] += sum(n) - sum(p[u]);
+
+    add(p[u], 1);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> p[i];
+
+        nums.emplace_back(p[i]);
+    }
+
+    std::sort(nums.begin(), nums.end());
+    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
+
+    for (int i = 1; i <= n; i++) {
+        p[i] = std::lower_bound(nums.begin(), nums.end(), p[i]) - nums.begin() + 1;
+    }
+
+    for (int i = 2, x; i <= n; i++) {
+        cin >> x;
+
+        g[x].emplace_back(i);
+    }
+
+    dfs(1);
+
+    for (int i = 1; i <= n; i++) {
+        cout << ans[i] << endl;
+    }
+
+    return 0;
+}