leetcode1627 带阈值的图连通性

思路：
埃氏筛法+并查集。
实现：
 1 class DSU
 2 {
 3     vector<int> p;
 4 public:
 5     DSU(int n)
 6     {
 7         p.resize(n);
 8         for (int i = 1; i < n; i++) p[i] = i;
 9     }
10     int find(int x)
11     {
12         if (p[x] == x) return x;
13         return p[x] = find(p[x]);
14     }
15     void uni(int x, int y)
16     {
17         x = find(x); y = find(y);
18         if (x != y) p[x] = y;
19     }
20 };
21 class Solution
22 {
23 public:
24     vector<bool> areConnected(int n, int threshold, vector<vector<int>>& queries)
25     {
26         vector<bool> v(n + 1, false);
27         DSU d(n + 1);
28         for (int i = threshold + 1; i <= n; i++)
29         {
30             if (v[i]) continue;
31             v[i] = true;
32             for (int j = 2 * i; j <= n; j += i)
33             {
34                 d.uni(i, j);
35                 v[j] = true;
36             }
37         }
38         vector<bool> res;
39         for (auto& q: queries)
40         {
41             if (d.find(q[0]) == d.find(q[1])) res.push_back(true);
42             else res.push_back(false);
43         }
44         return res;
45     }
46 };