#3751. 「SDOI2009」HH 的项链

https://loj.ac/s/1474109

LibreOJ/3751/3751.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 = 50005,
+          M = 200005,
+          S = 1e6 + 5;
+
+int n, m, a[N], c[S], t, ans[M];
+std::vector<std::tuple<int, int, int>> q;
+
+inline int get(int x) {
+    return x / t;
+}
+
+inline void add(int x, int& r) {
+    if (!c[x]++) r++;
+}
+
+inline void del(int x, int& r) {
+    if (!--c[x]) r--;
+}
+
+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 >> m;
+
+    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 = get(std::get<1>(a)),
+            q = get(std::get<1>(b));
+
+        return p == q ? std::get<2>(a) < std::get<2>(b) : p < q;
+    });
+
+    for (int k = 0, i = 0, j = 1, res = 0, id, l, r; k < q.size(); k++) {
+        std::tie(id, l, r) = q[k];
+
+        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;
+}