leetcode1627 带阈值的图连通性

思路：

埃氏筛法+并查集。

实现：

class DSU
{
    vector<int> p;
public:
    DSU(int n)
    {
        p.resize(n);
        for (int i = 1; i < n; i++) p[i] = i;
    }
    int find(int x)
    {
        if (p[x] == x) return x;
        return p[x] = find(p[x]);
    }
    void uni(int x, int y)
    {
        x = find(x); y = find(y);
        if (x != y) p[x] = y;
    }
};
class Solution
{
public:
    vector<bool> areConnected(int n, int threshold, vector<vector<int>>& queries)
    {
        vector<bool> v(n + 1, false);
        DSU d(n + 1);
        for (int i = threshold + 1; i <= n; i++)
        {
            if (v[i]) continue;
            v[i] = true;
            for (int j = 2 * i; j <= n; j += i)
            {
                d.uni(i, j);
                v[j] = true;
            }
        }
        vector<bool> res;
        for (auto& q: queries)
        {
            if (d.find(q[0]) == d.find(q[1])) res.push_back(true);
            else res.push_back(false);
        }
        return res;
    }
};