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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. const int MAXN = 100000; 
  5. int arr[MAXN];
  6. int tree[4*MAXN];
  7.  
  8. // Hàm gcd có sẵn trong <algorithm> (C++17) là std::__gcd(x, y);
  9.  
  10. void build_tree(int index, int start, int end) {
  11.     if (start == end) {
  12.         tree[index] = arr[start];
  13.         return;
  14.     }
  15.     int mid = (start + end) / 2;
  16.     build_tree(index*2, start, mid);
  17.     build_tree(index*2+1, mid+1, end);
  18.     tree[index] = std::__gcd(tree[index*2], tree[index*2+1]);
  19. }
  20.  
  21. int get_gcd(int index, int start, int end, int L, int R) {
  22.     if (end < L || start > R)  return 0;    // segment hoàn toàn ngoài [L, R]
  23.     if (L <= start && end <= R) return tree[index]; // segment nằm gọn trong [L, R]
  24.     int mid = (start + end) / 2;
  25.     int gcdLeft  = get_gcd(index*2, start, mid, L, R);
  26.     int gcdRight = get_gcd(index*2+1, mid+1, end, L, R);
  27.     return std::__gcd(gcdLeft, gcdRight);
  28. }
  29.  
  30. int main() {
  31.     ios::sync_with_stdio(false);
  32.     cin.tie(nullptr);
  33.  
  34.     int n, k;
  35.     cin >> n >> k;
  36.     for (int i = 0; i < n; i++) {
  37.         cin >> arr[i];
  38.     }
  39.  
  40.     // Xây cây segment
  41.     build_tree(1, 0, n-1);
  42.  
  43.     int ans = 1;
  44.     for (int start = 0; start <= n-k; start++) {
  45.         int g = get_gcd(1, 0, n-1, start, start + k - 1);
  46.         ans = max(ans, g);
  47.     }
  48.  
  49.     cout << ans << "\n";
  50.     return 0;
  51. }
  52.  
Success #stdin #stdout 0.01s 5284KB
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https://ideone.com/zEv23L
language:
C++14 (gcc 8.3)
created:
5 days ago
visibility:
public

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