P6824 「EZEC-4」可乐

R57971753

Luogu/problem/P6824/P6824.cpp

@@ -0,0 +1,54 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, k, a[1000005], ans;
+
+struct node {
+    int val;
+    node* next[2];
+
+    ~node() {
+        for (auto& i : next) {
+            delete i;
+        }
+    }
+};
+
+void insert(node* root, int x) {
+    for (int i = 21; i >= 0; i--) {
+        if (root->next[(x >> i) & 1] == nullptr) root->next[(x >> i) & 1] = new node();
+        root = root->next[(x >> i) & 1];
+        root->val++;
+    }
+}
+
+int search(node* root, int x) {
+    int res = 0;
+    node* p = root;
+    for (int i = 21; i >= 0; i--) {
+        int c = (x >> i) & 1;
+        int t = (k >> i) & 1;
+        if (t && p->next[1 - (c ^ t)] != nullptr) {
+            res += p->next[1 - (c ^ t)]->val;
+        }
+        if (p->next[c ^ t] == nullptr) break;
+        p = p->next[c ^ t];
+    }
+    return res;
+}
+
+int main() {
+    node* root = new node();
+    cin >> n >> k;
+    for (int i = 0; i < n; i++) {
+        cin >> a[i];
+        insert(root, a[i]);
+    }
+    for (int i = 0; i <= 2097151; i++) {
+        ans = max(ans, search(root, i));
+    }
+    cout << ans << endl;
+    delete root;
+    return 0;
+}