异或与最爱数字(XOR and Favorite Number) 题解

思路分析

按题目要求使用对应数据结构与算法模拟/递推求解，注意数据范围边界与时间复杂度。

参考代码

#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;

struct Query {
    int l, r, id, blk;
    bool operator<(const Query& o) const {
        if (blk != o.blk) return blk < o.blk;
        return (blk & 1) ? (r > o.r) : (r < o.r);
    }
};

int cnt[1 << 21];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m, k;
    if (!(cin >> n >> m >> k)) return 0;
    vector<int> pref(n + 1, 0);
    for (int i = 1; i <= n; ++i) {
        int a;
        cin >> a;
        pref[i] = pref[i - 1] ^ a;
    }
    int B = max(1, (int)(n / sqrt(max(1, m))));
    vector<Query> qs(m);
    for (int i = 0; i < m; ++i) {
        int l, r;
        cin >> l >> r;
        qs[i] = {l - 1, r, i, (l - 1) / B};
    }
    sort(qs.begin(), qs.end());
    long long curAns = 0;
    auto add = [&](int x) {
        curAns += cnt[x ^ k];
        cnt[x]++;
    };
    auto del = [&](int x) {
        cnt[x]--;
        curAns -= cnt[x ^ k];
    };
    int curL = 0, curR = -1;
    vector<long long> ans(m);
    for (const auto& qu : qs) {
        while (curL > qu.l) add(pref[--curL]);
        while (curR < qu.r) add(pref[++curR]);
        while (curL < qu.l) del(pref[curL++]);
        while (curR > qu.r) del(pref[curR--]);
        ans[qu.id] = curAns;
    }
    for (int i = 0; i < m; ++i) cout << ans[i] << "\n";
    return 0;
}