P3604 美好的每一天

https://www.luogu.com.cn/record/97840002

Luogu/P3604/P3604.cpp

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+#include <iostream>
+#include <algorithm>
+#include <cmath>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 6e4 + 5;
+
+int n, m, t, a[N], cnt[1 << 26], res, ans[N];
+std::string s;
+std::vector<std::tuple<int, int, int>> qs;
+
+void add(int x) {
+    res += cnt[a[x]]++;
+
+    for (int i = 0; i < 26; i++) {
+        res += cnt[a[x] ^ (1 << i)];
+    }
+}
+
+void del(int x) {
+    res -= --cnt[a[x]];
+
+    for (int i = 0; i < 26; i++) {
+        res -= cnt[a[x] ^ (1 << i)];
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> m >> s;
+
+    s = ' ' + s;
+
+    for (int i = 1; i <= n; i++) {
+        a[i + 1] = a[i] ^ (1 << (s[i] - 'a'));
+    }
+
+    for (int i = 1, l, r; i <= m; i++) {
+        cin >> l >> r;
+
+        qs.emplace_back(i, l, r + 1);
+    }
+
+    t = std::sqrt(n + 1);
+
+    std::sort(qs.begin(), qs.end(), [&](std::tuple<int, int, int> lhs, std::tuple<int, int, int> rhs) -> bool {
+        int p = std::get<1>(lhs) / t,
+            q = std::get<1>(rhs) / t;
+        int x = std::get<2>(lhs),
+            y = std::get<2>(rhs);
+
+        return p == q
+                 ? p & 1 ? x < y : x > y
+                 : p < q;
+    });
+
+    int i = 0, j = 1;
+
+    for (auto q : qs) {
+        int id, l, r;
+
+        std::tie(id, l, r) = q;
+
+        while (i < r) add(++i);
+        while (i > r) del(i--);
+        while (j < l) del(j++);
+        while (j > l) add(--j);
+
+        ans[id] = res;
+    }
+
+    for (int i = 1; i <= m; i++) {
+        cout << ans[i] << endl;
+    }
+
+    return 0;
+}