P5268 [SNOI2017]一个简单的询问

https://www.luogu.com.cn/record/76801640

Luogu/P5268/P5268.cpp

@@ -0,0 +1,73 @@
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+#include <tuple>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, q, a[N], c1[N], c2[N], t, ans[N];
+std::vector<std::tuple<int, int, int, int>> qs;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    t = sqrt(n);
+
+    cin >> q;
+
+    for (int i = 1, l1, r1, l2, r2; i <= q; i++) {
+        cin >> l1 >> r1 >> l2 >> r2;
+
+        qs.push_back(std::make_tuple(i, r1, r2, 1));
+        qs.push_back(std::make_tuple(i, r1, l2 - 1, -1));
+        qs.push_back(std::make_tuple(i, l1 - 1, r2, -1));
+        qs.push_back(std::make_tuple(i, l1 - 1, l2 - 1, 1));
+    }
+
+    std::for_each(qs.begin(), qs.end(), [&](auto &x) {
+        int &l = std::get<1>(x),
+            &r = std::get<2>(x);
+
+        if (l > r) std::swap(l, r);
+    });
+
+    std::sort(qs.begin(), qs.end(), [&](auto a, auto b) {
+        int p = std::get<1>(a) / t,
+            q = std::get<1>(b) / t;
+        int x = std::get<2>(a),
+            y = std::get<2>(b);
+
+        return p == q ? p & 1 ? x < y : x > y : p < q;
+    });
+
+    int i = 0, j = 0, res = 0;
+    for (auto &e : qs) {
+        int id, l, r, x;
+        std::tie(id, l, r, x) = e;
+
+        while (i < r) res += c1[a[++i]], c2[a[i]]++;
+        while (i > r) res -= c1[a[i]], c2[a[i--]]--;
+        while (j < l) res += c2[a[++j]], c1[a[j]]++;
+        while (j > l) res -= c2[a[j]], c1[a[j--]]--;
+
+        ans[id] += x * res;
+    }
+
+    for (int i = 1; i <= q; i++) {
+        cout << ans[i] << endl;
+    }
+
+    return 0;
+}