mirror of
https://git.sb/baoshuo/OI-codes.git
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126 lines
2.5 KiB
C++
126 lines
2.5 KiB
C++
#include <iostream>
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#include <functional>
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#include <numeric>
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#include <queue>
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#include <tuple>
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using std::cin;
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using std::cout;
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const char endl = '\n';
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const int N = 5e5 + 5;
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class Trie {
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private:
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const int len = 30;
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struct node {
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int cnt;
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node* child[2];
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node()
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: cnt(0), child{0, 0} {}
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~node() {
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if (child[0]) delete child[0];
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if (child[1]) delete child[1];
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}
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};
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node* root;
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public:
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Trie()
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: root(new node()) {}
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~Trie() {
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delete root;
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}
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void insert(unsigned long long val) {
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node* cur = root;
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cur->cnt++;
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for (int i = 32; ~i; i--) {
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bool x = (val >> i) & 1;
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if (cur->child[x] == nullptr) cur->child[x] = new node();
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cur = cur->child[x];
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cur->cnt++;
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}
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}
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unsigned long long query(unsigned long long val, int k) {
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node* cur = root;
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unsigned long long res = 0;
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for (int i = 32; ~i; i--) {
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bool x = (val >> i) & 1;
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if (cur->child[x] && cur->child[x]->cnt >= k) {
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cur = cur->child[x];
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} else {
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if (cur->child[x]) k -= cur->child[x]->cnt;
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cur = cur->child[x ^ 1];
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res |= 1ll << i;
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}
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}
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return res;
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}
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};
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int n, k;
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unsigned long long s[N], ans;
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std::priority_queue<
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std::tuple<int, int, unsigned long long>,
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std::vector<std::tuple<int, int, unsigned long long>>,
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auto(*)(std::tuple<int, int, unsigned long long>, std::tuple<int, int, unsigned long long>)->bool>
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q{[](std::tuple<int, int, unsigned long long> lhs, std::tuple<int, int, unsigned long long> rhs) -> bool {
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return std::get<2>(lhs) < std::get<2>(rhs);
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}};
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Trie trie;
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n >> k;
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k <<= 1;
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trie.insert(0);
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for (int i = 1; i <= n; i++) {
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unsigned long long x;
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cin >> x;
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s[i] = s[i - 1] ^ x;
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trie.insert(s[i]);
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}
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for (int i = 0; i <= n; i++) {
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q.emplace(i, n + 1, trie.query(s[i], n + 1));
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}
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while (k--) {
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auto t = q.top();
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q.pop();
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ans += std::get<2>(t);
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if (std::get<1>(t)) {
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q.emplace(
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std::get<0>(t),
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std::get<1>(t) - 1,
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trie.query(s[std::get<0>(t)], std::get<1>(t) - 1));
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}
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}
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cout << (ans >> 1) << endl;
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return 0;
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}
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