P2709 小B的询问

https://www.luogu.com.cn/record/76780844

Luogu/P2709/P2709.cpp

@@ -0,0 +1,72 @@
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+#include <tuple>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e4 + 5;
+
+int n, m, k, a[N], c[N], t, ans[N];
+std::vector<std::tuple<int, int, int>> q;
+
+inline void add(int x, int &res) {
+    res += 2 * c[x] + 1;
+    c[x]++;
+}
+
+inline void del(int x, int &res) {
+    res -= 2 * c[x] - 1;
+    c[x]--;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m >> k;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    t = sqrt(n);
+
+    for (int i = 1, l, r; i <= m; i++) {
+        cin >> l >> r;
+
+        q.push_back(std::make_tuple(i, l, r));
+    }
+
+    std::sort(q.begin(), q.end(), [&](auto a, auto b) {
+        int p = std::get<1>(a) / t,
+            q = std::get<1>(b) / t;
+
+        return p == q
+                 ? (p & 1)
+                     ? std::get<2>(a) < std::get<2>(b)
+                     : std::get<2>(a) > std::get<2>(b)
+                 : p < q;
+    });
+
+    int i = 0, j = 1, res = 0, id, l, r;
+    for (auto &e : q) {
+        std::tie(id, l, r) = e;
+
+        while (i < r) add(a[++i], res);
+        while (i > r) del(a[i--], res);
+        while (j < l) del(a[j++], res);
+        while (j > l) add(a[--j], res);
+
+        ans[id] = res;
+    }
+
+    for (int i = 1; i <= m; i++) {
+        cout << ans[i] << endl;
+    }
+
+    return 0;
+}